Don't escape Html in patches

Fixes #2036

app/controllers/commit_controller.rb

@@ -26,7 +26,7 @@ class CommitController < ProjectResourceController
         end
       end
 
-      format.patch
+      format.patch { render text: @commit.to_patch }
     end
   end
 end

app/views/commit/show.patch.erb

-<%= @commit.to_patch %>