Add "main" entry point to package.json
Add "main" entry point to package.json

This fixes an issue with requiring react-native-linear-gradient from @flow-ified
file, which used to produce "module not found" error.

react-native-community/react-native-linear-gradient,react-native-community/react-native-linear-gradient,react-native-community/react-native-linear-gradient,react-native-community/react-native-linear-gradient