Update Podspec for Xcode 12 Support

[daaashleywch]

Environment

Environment:
OS: macOS Big Sur 11.2.2
Node: 11.10.1
Yarn: 1.19.1
npm: 6.7
Watchman: 4.7.0
Xcode: Xcode 12.4 stable
Android Studio: NA

Packages: (wanted => installed)
react-native: 0.62.2 => 0.63.4 (current stable)
react: 16.13.1

Target Platforms:
iOS 9-11

Steps to Reproduce

Xcode 12 reveals a dependency issue for React Native in the Podspec file of every native library.

See this comment here on the React Native Repo: facebook/react-native#29633 (comment) . Notice following that comment all of the repos that that feed gets mentioned in, and how they all updated this dependency thereafter.

This change, s.dependency from 'React' to 'React-Core' is needed to get this module to compile correctly with react native in Xcode 12. Without this change, Xcode 12 fails to compile the library, at least with newer version of react native.

I currently have this patch and it works with Xcode 12: