title: Error:Jack is required to support java 8 language features
body: <p>When I tried to update my android project to use Java 8 after getting android studio 2.1 and android N SDK
  by adding </p>
  
  <pre><code>compileOptions {
      sourceCompatibility JavaVersion.VERSION_1_8
      targetCompatibility JavaVersion.VERSION_1_8
  }
  </code></pre>
  
  <p>I had this error </p>
  
  <blockquote>
    <p>Error:Jack is required to support java 8 language features. Either enable Jack or remove sourceCompatibility JavaVersion.VERSION_1_8.</p>
  </blockquote>
  
  <p>What should I do?</p>