build: temporary allow web crawler to netlify

- for web crawler to see X-Robots-Tag header
- https://www.bing.com/webmasters/help/?topicid=37c07477

netlify.toml

@@ -1,4 +1,4 @@
 [context.production]
   environment = { NODE_ENV = "production" }
   publish = "public"
-  command = "npm run build"
+  command = "npm run build && mv public/robots-mdleom.com.txt public/robots.txt"

source/_redirects

@@ -4,4 +4,3 @@
 # /screenshot/* https://cdn.statically.io/screenshot/device=mobile/curben.netlify.app/:splat 200
 /screenshot/* https://cdn.statically.io/screenshot/curben.netlify.app/:splat 200
 /files/* https://gitlab.com/curben/blog/-/raw/site/:splat 200
-/robots.txt /robots-mdleom.com.txt 200