title: Gradle Sync Failed - MissingPropertyException after upgrade to gradle 5.1
body: <p>Just updated to <code>Android Studio 3.3 RC 2</code> &amp; <code>gradle tools to 5.1</code>, it started to give the following <strong>error</strong>,</p>
  
  <pre><code>No such property: dir for class: org.gradle.api.internal.file.collections.DefaultConfigurableFileCollection
  * What went wrong:
  A problem occurred configuring project ':app'.
  &gt; groovy.lang.MissingPropertyException: No such property: dir for class: org.gradle.api.internal.file.collections.DefaultConfigurableFileCollection
  </code></pre>
  
  <p>Any idea what's the solution to this?</p>
  
  <p>I'm using<br>
  <code>com.android.tools.build:gradle:3.4.0-alpha08</code></p>