Use React-Core instead of React

We should depend on React-Core instead of React according to facebook/react-native#29633 (comment). You can check all the related PRs links to this issue.

Author: radko93

react-native-branch.podspec

@@ -23,7 +23,7 @@ Pod::Spec.new do |s|
   s.compiler_flags = %[-DRNBRANCH_VERSION=@\\"#{s.version}\\"]
   s.header_dir   = 'RNBranch' # also sets generated module name
   s.dependency 'Branch', '1.40.2'
-  s.dependency 'React' # to ensure the correct build order
+  s.dependency 'React-Core' # to ensure the correct build order
 
   # Swift/Objective-C compatibility
   s.pod_target_xcconfig = {