title: CardView: image's corners is not rounded in Android 4.3?
body: <p>Android Studio version: 2.3.3, Android 4.3</p>
  
  <p>I am using CardView and want to round image's corners.</p>
  
  <p><strong>Layout</strong>:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:card_view="http://schemas.android.com/apk/res-auto"
      android:layout_width="@dimen/card_width"
      android:layout_height="@dimen/card_width"
      android:layout_gravity="center"
      android:gravity="center"
      android:orientation="vertical"&gt;
      &lt;android.support.v7.widget.CardView
          android:id="@+id/card_view"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:layout_gravity="center"
          card_view:cardCornerRadius="15dp"&gt;
  
          &lt;RelativeLayout
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:layout_gravity="center"&gt;
              &lt;ImageView
                  android:layout_width="match_parent"
                  android:layout_height="match_parent"
                  android:scaleType="centerCrop"
                  android:src="@drawable/img_lights" /&gt;
          &lt;/RelativeLayout&gt;
      &lt;/android.support.v7.widget.CardView&gt;
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>As you can ses I set </p>
  
  <p><code>card_view:cardCornerRadius="15dp</code></p>
  
  <p><strong>Here is the result:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/kURU8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/kURU8.png" alt="Not round image"></a></p>
  
  <p>But image's corners is not rounded. Why?</p>