All com.android.support libraries must use the exact same version specification


Androidアプリにadmobの広告を入れようとして、build.gradleに

implementation 'com.android.support:appcompat-v7:27.+'
implementation 'com.google.android.gms:play-services-ads:17.2.0'

と記述したら、ライブラリの中に27.1.1と26.1.0が混在していて、customtabsのバージョンが合ってないと怒られる...

All com.android.support libraries must use the exact same version specification (mixing versions can lead to runtime crashes). Found versions 27.1.1, 26.1.0. Examples include com.android.support:animated-vector-drawable:27.1.1 and com.android.support:customtabs:26.1.0 less... (⌘F1) 
Inspection info:There are some combinations of libraries, or tools and libraries, that are incompatible, or can lead to bugs. One such incompatibility is compiling with a version of the Android support libraries that is not the latest version (or in particular, a version lower than your targetSdkVersion).  Issue id: GradleCompatible

customtabsのバージョンを個別に記述して解決する

implementation 'com.android.support:appcompat-v7:27.+'
implementation 'com.google.android.gms:play-services-ads:17.2.0'
implementation 'com.android.support:customtabs:27.1.1'