title: Could not get unknown property 'ANDROID_SUPPORT_VERSION' for project ':demo' of type org.gradle.api.Project
body: <p>I am trying to use this library : <a href="https://github.com/telly/MrVector" rel="nofollow noreferrer">https://github.com/telly/MrVector</a> in my android studio project.
  So what I did is to import it as a module in my project and when i tried to sync project 
  this error appeared </p>
  
  <blockquote>
    <p>Could not get unknown property 'ANDROID_SUPPORT_VERSION' for project ':demo' of type org.gradle.api.Project.</p>
  </blockquote>
  
  <p>Here is where the problem occurs in the Gradle file:</p>
  
  <pre><code>dependencies {
    compile project(':library')
    compile "com.android.support:appcompat-v7:${project.ANDROID_SUPPORT_VERSION}@aar"
  }
  </code></pre>