title: Native-Base Picker does not work properly Android - Does not trigger function onValueChange
body: <p>I'm using <code>Picker</code> component of <code>Native-Base</code> for my <code>react-native</code> application. On IOS everything is ok, whereas, on <code>Android</code> side I can not trigger function I added on <code>onValueChange</code>.</p>
  
  <p>Is there anyone faced this issue before?</p>
  
  <p>How did you fix it? I stuck here almost a day.</p>
  
  <p>Here is my code.</p>
  
  <pre><code>&lt;Picker style={{ width: 200, height: 40}}
                                      iosHeader="Branch"
                                      Header="Branch"
                                      mode="dropdown"
                                      textStyle={{color: 'white'}}
                                      placeholder="Branch"
                                      headerBackButtonText="Geri"
                                      selectedValue={this.state.selectedBranch}
                                      onValueChange={(value)=&gt;this.onBranchSelected(value)}
                                  &gt;
                                      {this.state.branches.map((branches, i)=&gt;{
                                              return(
                                                  &lt;Picker.Item label={branches.address_line} value={branches.id} key={i}/&gt;
                                              );
                                          }
                                      )}
                                  &lt;/Picker&gt;
  </code></pre>
  
  <p>It does not call the function <code>onBranchSelected</code> on Android.</p>