add MobileCoreServices framework (#338)

this fixes IOS Build error: Undefined symbol: _kUTTypeJPEG, Undefined symbol: _kUTTypePNG
these symobls are defined in MobileCoreServices library, so the lib must
be linked in the podspec

the build error can be reproduced when using use_frameworks! in project
Podfile that has react-native-image-resizer as a dependency

Author: tautvilas

react-native-image-resizer.podspec

@@ -18,7 +18,7 @@ Pod::Spec.new do |s|
   s.source_files = "ios/**/*.{h,m,mm}"
 
   s.dependency "React-Core"
-  s.ios.framework = 'AssetsLibrary'
+  s.ios.framework = 'AssetsLibrary', 'MobileCoreServices'
 
   # Don't install the dependencies when we run `pod install` in the old architecture.
   if ENV['RCT_NEW_ARCH_ENABLED'] == '1' then