title: android studio import .aar in library module not app module
body: <p>I want import .arr in my library module not main module,how can i do?<br/>
  in my library module build.gradle set aar, err: can not find it.</p>
  
  <pre><code>dependencies {
      compile(name:'nameArrFile', ext:'aar')
  }
  
  repositories{
      flatDir{
          dirs 'libs'
      }
  }
  </code></pre>