title: Android Studio - error: cannot find symbol class FirebaseAuth
body: <p>I'm getting these errors in Android: </p>
  
  <pre><code>error: cannot find symbol class FirebaseAuth
  error: cannot find symbol variable FirebaseAuth
  error: cannot find symbol class OnCompleteListener
  error: cannot find symbol class AuthResult
  </code></pre>
  
  <p>My build.gradle in app: </p>
  
  <pre><code>implementation 'com.google.firebase:firebase-auth:16.1.0'
  implementation 'com.google.firebase:firebase-core:16.0.7'
  </code></pre>
  
  <p>My build.gradle in project:</p>
  
  <pre><code>classpath 'com.google.gms:google-services:4.1.0'
  </code></pre>