Exclude a bunch of things from Jekyll generation.

In particular, the `vendor` directory where bundle recommends to
install dependencies.

Author: sjrd

_config.yml

@@ -10,9 +10,16 @@ analytics: #Google analytics code in the format XX-nnnnnnnn-n
 # baseurl: ""
 baseurl: ""
 url: "https://www.scala-js.org"
-exclude: ["*.iml"]
 production_url: "https://www.scala-js.org"
 
+exclude:
+  - "*.iml"
+  - Gemfile
+  - Gemfile.lock
+  - README.md
+  - Rakefile
+  - vendor
+
 assets:
   prefix: "/assets"
   digest: true