[Bug Fix] Header Style on IOS

[broerjuang]

I try to tackle the issue on #116 . I think it's because the headerStyle props never get passed to SafeAreaView.
So, here's the result after I define the style on Home.

    <StackNavigator.Screen
      headerTitle="Homes"
      navigation=nav
      headerStyle=Style.(style([backgroundColor(String("red"))]))>
      ...(
           () =>
             <View style=Styles.continer>
               <Text style=Styles.title>
                 (ReasonReact.string("Home screen"))
               </Text>
               (renderButtons(nav))
             </View>
         )
    </StackNavigator.Screen>,

[knowbody]

Thank you!