64bit support on Android now ready for testing

Those of you running React Native >= 0.58 may have run into an issue when trying to make 64bit builds while using this plugin. Cry no more, this PR should fix that! https://github.com/oney/react-native-webrtc/pull/602

Please give it a go and provide feedback so we are sure everything is OK before landing the patch. Thanks!

PS: The WebRTC version remains the same, M69.