fix: Xcode 12 compatibility (#146)

Author: r3nya

react-native-print.podspec

@@ -15,5 +15,5 @@ Pod::Spec.new do |s|
   s.source          = { :git => "https://github.com/christopherdro/react-native-print", :tag => "v#{s.version}" }
   s.source_files    = 'ios/**/*.{h,m}'
 
-  s.dependency 'React'
+  s.dependency 'React-Core'
 end