title: Add Google Mobile Vision library dependency to gradle
body: <p>
  i want to add google mobile vision library by add this line to build.gradle :</p>
  
  <p>compile 'com.google.android.gms:play-services-vision:11.6.0'</p>
  
  <p>but android studio error!</p>
  
  <p>what's wrong?</p>