ihara2525/marks — pull request #9 by dex1t (2014-12-16 12:16:23+00:00)
Title: Fix bug that marked_by? returns true when other user marked

`#marked_by?` method returns ```true``` when someone marks the object.
But I think this method should return ```false``` when the other user marked.
@ihara2525 please review this pr :eyes: