title: Android Studio: "could not find method compile<> for arguments [file collection]"
body: <p>I am trying to add <code>aws-android-sdk-1.6.1-debug.jar</code> (Amazon Cloud Service) library to my Android Studio project.
  So I copied the jar-file to libs-directory, right clicked "Add as library".
  Then added the line compile files(<code>libs/aws-android-sdk-1.6.1-debug.jar</code>) to the <code>build.gradle</code> file and run <code>gradlew</code> clean bat from command prompt.
  This bat gives error:</p>
  
  <pre><code>"could not find method compile&lt;&gt; for arguments [file collection]"
  </code></pre>
  
  <p>Even though the jar-file surely is in the libs-directory.
  I also tried: <code>compile fileTree(dir: 'libs', include: '*.jar')</code> with the same result.
  Build in Android Studio gives the same result.</p>
  
  <p>Why the jar could not be found ?</p>