fix(ios): Xcode 12 compatibility (#229)

Author: troZee

react-native-viewpager.podspec

@@ -16,5 +16,5 @@ Pod::Spec.new do |s|
   s.source_files  = "ios/**/*.{h,m}"
   s.requires_arc = true
 
-  s.dependency "React"
+  s.dependency 'React-Core'
 end