Update moment to fix #597
Update moment to fix #597

Basically, the `metro-bundler` never accepted the way moment worked with dynamic imports. But 2.19.0 fixes that and allows the lib to be used on RN >=49.0.

Read here for [more details](https://github.com/facebook/metro-bundler/issues/65#issuecomment-335524547).
Chatnbook/react-native-gifted-chat,Chatnbook/react-native-gifted-chat,FaridSafi/react-native-gifted-chat,ianlin/react-native-gifted-messenger,ianlin/react-native-gifted-messenger,FaridSafi/react-native-gifted-chat,atFriendly/react-native-friendly-chat,atFriendly/react-native-friendly-chat,FaridSafi/react-native-gifted-messenger,atFriendly/react-native-friendly-chat,Chatnbook/react-native-gifted-chat,atFriendly/react-native-friendly-chat,FaridSafi/react-native-gifted-messenger