Fix error with reopened merge request not properly reloading

If you reopen a Merge Request and then try to update the source branch
it won't properly reload the code since the "reload_code" method still
checks if the MR is "opened" and not just "open" (which includes reopened)

app/models/merge_request.rb

@@ -133,7 +133,7 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def reload_code
-    if merge_request_diff && opened?
+    if merge_request_diff && open?
       merge_request_diff.reload_content
     end
   end