Fix commit image js

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/javascripts/commit.js.coffee

 class Commit
   constructor: ->
-    $('.files .file').each ->
+    $('.files .diff-file').each ->
       new CommitFile(this)
 
 @Commit = Commit