12.2.0-1: fix(android): prevent breaking builds for react native 0.57

The android package 'io.intercom.android:intercom-sdk-base' version 5.1.6 introduced a breaking change.. (Come on people! Learn semantic versioning). More specifically it uses version 28 of com.android.support:appcompat-v7. This causes a problem for people using react native 0.57, because it uses version 27. So we lock down intercom-sdk-base to version 5.1.5 to stay on version 27 of com.android.support:appcompat-v7.