Clean up .gitignore. (#28050)

.gitignore

 # Ignore docs files
-_gh_pages
-_site
-site/docs/**/dist/
+/_gh_pages/
+/site/.jekyll-metadata
+/site/docs/**/dist/
 
-# Ignore ruby files
-.ruby-version
-.bundle
-vendor/cache
-vendor/bundle
+# Ignore ruby/bundler files
+/.bundle/
+/vendor/
+/.ruby-version
 
 # Numerous always-ignore extensions
 *.diff
@@ -39,9 +38,6 @@ Thumbs.db
 .komodotools
 *.komodoproject
 
-# Jekyll metadata
-docs/.jekyll-metadata
-
 # Folders to ignore
-node_modules
-js/coverage
+/js/coverage/
+/node_modules/