Fixed merge request diff page after back browser button is pressed.

app/assets/javascripts/merge_request.js.coffee

@@ -123,7 +123,7 @@ class @MergeRequest
   loadDiff: (event) ->
     $.ajax
       type: 'GET'
-      url: this.$('.merge-request-tabs .diffs-tab a').attr('href')
+      url: this.$('.merge-request-tabs .diffs-tab a').attr('href') + ".json";
       beforeSend: =>
         this.$('.mr-loading-status .loading').show()
       complete: =>