RELEASING.md

1. Update to the latest SDK versions in build.js, RNPurchases.podspec and android/build.gradle.
2. Update versions in VERSIONS.md.
3. Update version in package.json.
4. Update platformFlavorVersion in RNPurchases.m.
5. Update versionName in android/build.gradle.
6. Add an entry to CHANGELOG.md
7. Run npm run build
8. git commit -am "Preparing for version x.y.z"
9. git tag x.y.z
10. git push origin master && git push --tags
11. Create a new release in github and upload
12. npm publish