Auto-update dependencies. (#877)

Author: dpebot

admob/app/build.gradle

@@ -40,7 +40,7 @@ dependencies {
  implementation 'com.android.support:customtabs:28.0.0'
 
  // [START gradle_play_config]
- implementation 'com.google.firebase:firebase-ads:17.2.0'
+ implementation 'com.google.firebase:firebase-ads:17.2.1'
  // [END gradle_play_config]
  implementation 'com.google.firebase:firebase-core:16.0.9'