Specify language detection for highlight.js

Because I am tired of CHANGELOG highlighted as sql file :)
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/helpers/blob_helper.rb

+module BlobHelper
+  def highlightjs_class(blob_name)
+    if blob_name.include?('.')
+      ext = blob_name.split('.').last
+      return 'language-' + ext
+    else
+      if no_highlight_files.include?(blob_name.downcase)
+        'no-highlight'
+      else
+        blob_name.downcase
+      end
+    end
+  end
+
+  def no_highlight_files
+    %w(credits changelog copying copyright license authors)
+  end
+end

app/views/shared/_file_hljs.html.haml

@@ -8,5 +8,5 @@
         = i
   .highlight
     %pre
-      %code
+      %code{ class: highlightjs_class(blob.name) }
         = blob.data