Fix for iOS7
Fix for iOS7

When using the banner in iOS7 an additional `layoutIfNeeded()` call is required as iOS7 doesn't handle this internally.

The exception this resolves is:
```
Auto Layout still required after executing -layoutSubviews. Banner's implementation of -layoutSubviews needs to call super.
```
bryx-inc/BRYXBanner,bryx-inc/BRYXBanner