title: android studio 3.1: build:gradle:3.1.0 - Absolute path are not supported when setting an output file name
body: <p>When I use Android Studio <strong>3.0</strong> and  I use the next version of <strong>Android Gradle Plugin</strong> in <code>project/build.gradle</code>:</p>
  
  <pre><code>classpath 'com.android.tools.build:gradle:3.0.1'
  </code></pre>
  
  <p>And it's work fine.
  After I update to Android Studio <strong>3.1</strong> , as result I update <strong>Android Gradle Plugin</strong> :</p>
  
  <pre><code>classpath 'com.android.tools.build:gradle:3.1.0'
  </code></pre>
  
  <p>And now I get error in my <code>app/build.gradle</code>:</p>
  
  <pre><code>def releaseFileName = "${rootProject.name}_${defaultConfig.versionName}.apk"
  outputFileName = new File(rootProject.projectDir.absolutePath + "/release", releaseFileName.toLowerCase())
  </code></pre>
  
  <p>Error: </p>
  
  <p><strong><em>Absolute path are not supported when setting an output file name</em></strong> </p>
  
  <p>I need to put output apk (<code>app-release.apk</code>) in specific path in project. In folder <code>MyProject/release/app-relese.apk</code>. How I can do this? </p>