Fix Xcode 12 compatibility (#143)

* Fix Xcode 12 compatibility

Compilation fails on Xcode 12 with `Undefined symbols for architecture` errors, due to the React dependency in the podspec.

See the react-native issue here - facebook/react-native#29633 (comment)

* Update react-native-restart.podspec

Author: Adrian Stein

react-native-restart.podspec

@@ -15,5 +15,5 @@ Pod::Spec.new do |s|
 
   s.source_files = "ios/**/*.{h,m}"
 
-  s.dependency "React"
+  s.dependency "React-Core"
 end