Fix for issue building QuickDialog with CocoaPods

I was trying to use QuickDialog with CocoaPods and RubyMotion, but I'd get an error at the end of compilation:

Stack dump:
0.      :4:1: current parser token 'void'
/System/Library/BridgeSupport/ruby-1.8/bridgesupportparser.rb:960: [BUG] Segmentation fault

Apparently the gen_bridge_metadata command was running into an error parsing QuickDialog's header files. I did some debugging and was able to narrow down the problem to QImageElement.h. I'm new to Objective-C, but it appears that the type was listed twice, both as enum and UIImagePickerControllerSourceType. The attached change fixes the problem and allows the QuickDialog pod to build successfully.