title: React Native TextInput not updating state
body: <p>Well this is an embarrassing question, but I can't get this TextInput to take values I type into it.</p>
  
  <p>It just deletes it as fast as I can type it - and I'm pretty sure logging this.state.code shows an empty variable.</p>
  
  <p>Is it the keyboard type messing with me? Do I need to do a  <code>.toString()</code>?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>constructor() {
      super()
      this.state = {
          code: '12'
      }
  }
  
  &lt;TextInput
      onChangedText={(text) =&gt; this.setState({code: text})}
      value={this.state.code}
      keyboardType='numeric'
      style={styles.input}
      placeholder='Code'
      maxLength={4}
  /&gt;</code></pre>
  </div>
  </div>
  </p>