diff --git a/.travis.yml b/.travis.yml
index cc41384..069f88a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,19 +1,23 @@
+dist: bionic
+sudo: false
+
 language: node_js
 node_js:
-  - "node" # latest stable Node.js release
+  - "node"
 
 cache:
-  directories:
-    - "node_modules" # cache the modules for faster build
+  npm: true
 
 script:
-  - npm install -g snyk
-  - npm install # install node modules
+  - npm install snyk
   - snyk auth $SNYK_TOKEN
   - snyk test # Check node modules for vulnerability
   - snyk protect # Patch node modules (if available)
   - snyk monitor # Update dependencies to snyk
 
+  - npm install standard
+  - standard
+
 branches:
   only:
   - master # Only build master branch
diff --git a/lib/filter.js b/lib/filter.js
index 1ee9620..d2ec9e1 100644
--- a/lib/filter.js
+++ b/lib/filter.js
@@ -33,10 +33,10 @@ function logicHtml (str, data) {
   // Return if a path matches exclusion pattern
   if (isMatch(path, exclude, globOptions)) return str
 
-  let result = Htmlminifier(str, options)
-  let saved = ((str.length - result.length) / str.length * 100).toFixed(2)
+  const result = Htmlminifier(str, options)
+  const saved = ((str.length - result.length) / str.length * 100).toFixed(2)
   if (options.logger) {
-    let log = hexo.log || console.log
+    const log = hexo.log || console.log
     log.log('Minify the html: %s [%s saved]', path, saved + '%')
   }
   return result
@@ -60,10 +60,10 @@ function logicCss (str, data) {
   return new Promise((resolve, reject) => {
     new CleanCSS(options).minify(str, (err, result) => {
       if (err) return reject(err)
-      let saved = ((str.length - result.styles.length) / str.length * 100).toFixed(2)
+      const saved = ((str.length - result.styles.length) / str.length * 100).toFixed(2)
       resolve(result.styles)
       if (options.logger) {
-        let log = hexo.log || console.log
+        const log = hexo.log || console.log
         log.log('Minify the css: %s [%s saved]', path, saved + '%')
       }
     })
@@ -92,10 +92,10 @@ function logicJs (str, data) {
   delete jsOptions.logger
   delete jsOptions.globOptions
 
-  let result = Terser.minify(str, jsOptions)
-  let saved = ((str.length - result.code.length) / str.length * 100).toFixed(2)
+  const result = Terser.minify(str, jsOptions)
+  const saved = ((str.length - result.code.length) / str.length * 100).toFixed(2)
   if (options.logger) {
-    let log = hexo.log || console.log
+    const log = hexo.log || console.log
     log.log('Minify the js: %s [%s saved]', path, saved + '%')
   }
   return result.code
@@ -107,9 +107,9 @@ function logicSvg () {
   // Return if disabled.
   if (options.enable === false) return
 
-  let route = hexo.route
-  let routeList = route.list()
-  let include = options.include
+  const route = hexo.route
+  const routeList = route.list()
+  const include = options.include
   const globOptions = options.globOptions
 
   let includeString = include
@@ -119,7 +119,7 @@ function logicSvg () {
   return Promise.all((micromatch(routeList, include, globOptions)).map(path => {
     return new Promise((resolve, reject) => {
       // Grab all assets using hexo router
-      let assetPath = route.get(path)
+      const assetPath = route.get(path)
       let assetTxt = ''
       // Extract the content
       assetPath.on('data', (chunk) => (assetTxt += chunk))
@@ -130,9 +130,9 @@ function logicSvg () {
             // Replace the original file with the minified.
             route.set(path, result.data)
             // Logging
-            let saved = ((assetTxt.length - result.data.length) / assetTxt.length * 100).toFixed(2)
+            const saved = ((assetTxt.length - result.data.length) / assetTxt.length * 100).toFixed(2)
             if (options.logger) {
-              let log = hexo.log || console.log
+              const log = hexo.log || console.log
               log.log('Minify the svg: %s [%s saved]', path, saved + '%')
             }
             resolve(assetTxt)
@@ -149,9 +149,9 @@ function logicGzip () {
   // Return if disabled.
   if (options.enable === false) return
 
-  let route = hexo.route
-  let routeList = route.list()
-  let include = options.include
+  const route = hexo.route
+  const routeList = route.list()
+  const include = options.include
   const globOptions = options.globOptions
 
   let includeString = include
@@ -161,7 +161,7 @@ function logicGzip () {
   return Promise.all((micromatch(routeList, include, globOptions)).map(path => {
     return new Promise((resolve, reject) => {
       // Grab all assets using hexo router
-      let assetPath = route.get(path)
+      const assetPath = route.get(path)
       let assetTxt = ''
       // Extract the content
       assetPath.on('data', (chunk) => (assetTxt += chunk))
@@ -173,9 +173,9 @@ function logicGzip () {
               // Save the compressed file to .gz
               route.set(path + '.gz', Input)
               // Logging
-              let saved = ((assetTxt.length - Input.toString().length) / assetTxt.length * 100).toFixed(2)
+              const saved = ((assetTxt.length - Input.toString().length) / assetTxt.length * 100).toFixed(2)
               if (options.logger) {
-                let log = hexo.log || console.log
+                const log = hexo.log || console.log
                 log.log('Gzip-compressed %s [%s saved]', path, saved + '%')
               }
               resolve(assetTxt)
@@ -195,9 +195,9 @@ function logicBrotli () {
   // Return if disabled.
   if (options.enable === false) return
 
-  let route = hexo.route
-  let routeList = route.list()
-  let include = options.include
+  const route = hexo.route
+  const routeList = route.list()
+  const include = options.include
   const globOptions = options.globOptions
 
   let includeString = include
@@ -207,23 +207,23 @@ function logicBrotli () {
   return Promise.all((micromatch(routeList, include, globOptions)).map(path => {
     return new Promise((resolve, reject) => {
       // Grab all assets using hexo router
-      let assetPath = route.get(path)
+      const assetPath = route.get(path)
       let assetTxt = ''
       // Extract the content
       assetPath.on('data', (chunk) => (assetTxt += chunk))
       assetPath.on('end', () => {
         if (assetTxt.length) {
           // Input has to be buffer for brotli
-          let input = Buffer.from(assetTxt, 'utf-8')
+          const input = Buffer.from(assetTxt, 'utf-8')
           // brotli defaults to max compression level
           br.compress(input, (err, output) => {
             if (!err) {
               // Save the compressed file to .br
               route.set(path + '.br', output)
               // Logging
-              let saved = ((input.length - output.toString().length) / input.length * 100).toFixed(2)
+              const saved = ((input.length - output.toString().length) / input.length * 100).toFixed(2)
               if (options.logger) {
-                let log = hexo.log || console.log
+                const log = hexo.log || console.log
                 log.log('Brotli-compressed %s [%s saved]', path, saved + '%')
               }
               resolve(assetTxt)