Update float to CGFloat for future proofing code (32-bit vs. 64-bit)

Apple recommends changing `float` to `CGFloat` with the introduction of the 64-bit CPU, as the `float` get's typedef'ed depending on the CPU type.

Apple recommends using the `CGFloat` "type" consistently in the documentation since the introduction of the 64-bit CPUs, and since UAProgressView currently uses `float` for "progress," many developers that have started using `CGFloat` (as well as NSInteger) in their applications will no longer be consistent.

https://developer.apple.com/library/ios/documentation/General/Conceptual/CocoaTouch64BitGuide/ConvertingYourAppto64-Bit/ConvertingYourAppto64-Bit.html

Since this will be an interface change, a new pod should be rolled out as well with the update.