Fix bug in persist callback for Rails 4.1

I noticed a couple of days back when using the fork that introduced this change, that my code did not run anymore, my spec were failing, testing use rails server failed. I tested just now with master and have the same problem. Looking at the new code I saw that where persist previously had a ```'result==true'``` (look at line 71), it now has ```result==false```. Changing this resolves the problem.