title: react-native: borderRadius does not frame component right
body: <p>The <code>borderRadius</code> style attribute doesn't change the border of a component correctly.</p>
  
  <p>I would expect to see a green circle on the red background without any white space. Instead, I see this.</p>
  
  <p><a href="https://i.stack.imgur.com/joyTO.png" rel="noreferrer"><img src="https://i.stack.imgur.com/joyTO.png" alt="enter image description here"></a></p>
  
  <pre><code>class Healthie extends React.Component {
    render() {
      return (
        &lt;View style={styles.container}&gt;
          &lt;Text style={styles.button} /&gt;
        &lt;/View&gt;
      );
    }
  };
  
  const styles = StyleSheet.create({
    container: {
      flex: 1,
      justifyContent: 'center',
      alignItems: 'center',
      backgroundColor: 'red',
    },
    button: {
      backgroundColor: 'green',
      borderRadius: 50,
      width: 100,
      height: 100,
      textAlign: 'center'
    }
  });
  </code></pre>
  
  <p>react-native version: 0.17.0.</p>