Better version tracking on Mapbox.framework downloads
Better version tracking on Mapbox.framework downloads

Added a `.framework_version` file to check against and only delete and re-download the Mapbox.framework when the version has changed.
bsudekum/react-native-mapbox-gl,bsudekum/react-native-mapbox-gl,bsudekum/react-native-mapbox-gl,bsudekum/react-native-mapbox-gl