title: When I use secureTextEntry = {true} the input reset the value when try to type again
body: <p>I'm using react native TextInput field for save a password value, so I added the <code>secureTextEntry</code> to hide the value. So I type the password and everything is good but if I go to other field let say username and I go back to the password and I want to add a new character to the password that I put it before the input gets clear and take the new character as the new password. So for example if I type "cat" and then I want to add another letter for example "o" it does not add like this: "cato" instead just set the value to "o"</p>
  
  <p>I'm using the <code>onChangeText</code> to handle the state but I dont know what is happening there..  </p>
  
  <p>This is the input:</p>
  
  <pre><code>&lt;TextInput onChangeText = {(pass) =&gt; this.setState({pass})} value = {this.state.pass} secureTextEntry = {true} /&gt;
  </code></pre>