feat: switch to terser for ES6 compatibility

lib/filter.js

@@ -1,7 +1,7 @@
 /* global hexo */
 'use strict'
 const CleanCSS = require('clean-css')
-const UglifyJS = require('uglify-js')
+const Terser = require('terser')
 const Htmlminifier = require('html-minifier').minify
 const Promise = require('bluebird')
 const minimatch = require('minimatch')
@@ -78,13 +78,13 @@ function logicJs (str, data) {
     }
   }
 
-  // uglifyjs doesn't like unsupported options
+  // Terser doesn't like unsupported options
   delete options.enable
   delete options.exclude
   let jsLogger = options.logger
   delete options.logger
 
-  let result = UglifyJS.minify(str, options)
+  let result = Terser.minify(str, options)
   let saved = ((str.length - result.code.length) / str.length * 100).toFixed(2)
   if (jsLogger) {
     let log = hexo.log || console.log

package.json

@@ -23,7 +23,7 @@
     "html-minifier": "^4.0.0",
     "iltorb": "^2.4.2",
     "minimatch": "^3.0.4",
-    "uglify-js": "^3.5.3"
+    "terser": "^3.17.0"
   },
   "keywords": [
     "html",