title: React Native FlatList separator between columns
body: <p>I have a FlatList with multiple columns:</p>
  
  <pre><code>    &lt;FlatList
        numColumns={4}
        ItemSeparatorComponent={this.renderSeparator}
        ...
      &lt;/FlatList&gt;
  </code></pre>
  
  <p>And a line separator:</p>
  
  <pre><code>  renderSeparator = () =&gt; (
      &lt;View
        style={{
          backgroundColor: 'red',
          height: 0.5,
        }}
      /&gt;
    );
  </code></pre>
  
  <p>But the separator only appear between rows, not between columns (even if i add             <code>width: 0.5</code></p>
  
  <p><a href="https://snack.expo.io/r171a0PwZ" rel="noreferrer">View on expo</a></p>