title: Mixing versions can lead to runtime crashes after adding admob ads library
body: <p>I Know there are many question like this, but didn't find any one with Admob ads  dependency, i just want to use Admob ads in my app, and i added the ads-dependency from official website <code>implementation 'com.google.android.gms:play-services-ads:15.0.0'</code>.</p>
  
  <p>But shows me this warning:</p>
  
  <pre><code>All gms/firebase libraries must use the exact same version specification (mixing versions can lead to runtime crashes). Found versions 15.0.1, 15.0.0. Examples include com.google.android.gms:play-services-ads-identifier:15.0.1   and com.google.android.gms:play-services-ads:15.0.0 less... (Ctrl+F1) 
  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.)
  </code></pre>
  
  <p>I only want to use ads dependency only without the firebase.</p>