title: Can't set visibility on constraint group
body: <p>When i try to set the visibility of the group on button click,it doesn't affect the view's visibility.Using com.android.support.constraint:constraint-layout:1.1.0-beta4. I've tried setting it element-wise without problems,but no success with the group. </p>
  
  <p><strong>My MainActivity.kt</strong></p>
  
  <pre><code>private fun toggleLoginUI(show: Boolean) {
      if (show) {
          group.visibility = VISIBLE
      } else {
          group.visibility = INVISIBLE
      }
  }
  
  fun onClick(view: View) {
      when (view.id) {
          R.id.button -&gt; toggleLoginUI(true)
          R.id.button4 -&gt; toggleLoginUI(false)
      }
  }
  </code></pre>
  
  <p><strong>My activity_main.xml</strong></p>
  
  <pre><code>    &lt;android.support.constraint.ConstraintLayout..
  
              &lt;TextView
                  android:id="@+id/textView"
  ... /&gt;
  
              &lt;TextView
                  android:id="@+id/textView2"
  ... /&gt;
  
              &lt;Button
                  android:id="@+id/button"
  .../&gt;
  
              &lt;Button
                  android:id="@+id/button4"
  ... /&gt;
  
  
              &lt;android.support.constraint.Group
                  android:id="@+id/group"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content"
                  android:visibility="visible"
                  app:constraint_referenced_ids="textView,textView2" /&gt;
              &lt;/android.support.constraint.ConstraintLayout&gt;
  </code></pre>