Upgrade dsl plugin. (#2772)
Upgrade dsl plugin. (#2772)

Gradle 5.6.4 expects the plugin to be version 1.2.9.
firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk,firebase/firebase-android-sdk