[MenuBundle] Fix typo Persistant/Persistent

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | N/A

http://www.thefreedictionary.com/persistent

Sorry, my last PR wasn't based on the 1.0 branch... I didn't see the note in contributing.md...