Fix flash message on devise view

It closes #385.

![screen shot 2014-06-13 at 6 03 01 pm](https://cloud.githubusercontent.com/assets/230476/3272821/b6b0b8ea-f31c-11e3-9166-c6fef294c72b.png)

Removing this scope for `#devise-flash-message` for give you the same result with one less selector.