title: How can change height and position of createBottomTabNavigator
body: <p>I have a createBottomTabNavigator on my project.by default tabs have specific height and bottom position .
  how can I change position and height of it
  my code:</p>
  
  <pre><code>const Navigate=createBottomTabNavigator({
      Home:{screen:Home,navigationOptions:{  
            tabBarLabel:'Home',  
            tabBarIcon:({tintColor})=&gt;(  
                &lt;Icon name="md-home" color={tintColor} size={25}/&gt;  
            )  
          }  },
      Camera:{screen:Camera,navigationOptions:{  
            tabBarLabel:'Profile',  
            tabBarIcon:({tintColor})=&gt;(  
                &lt;Icon name="md-add-circle" color={tintColor} size={25}/&gt;  
            )  
          } },
       Profile: {  
          screen:Profile,  
          navigationOptions:{  
            tabBarLabel:'Profile',  
            tabBarIcon:({tintColor})=&gt;(  
                &lt;Icon name="md-person" color={tintColor} size={25}/&gt;  
            )  
          }  
        },
  }
  ,{
      tabBarOptions: {
        activeTintColor: 'red',
        inactiveTintColor: 'cyan',
        activeBackgroundColor:'lightgreen',
        showLabel:false,
        keyboardHidesTabBar:false,
        tabStyle:{
              backgroundColor:'orange',
              height:40,
        },
      },
    },
    },
  );
  </code></pre>
  
  <p>export default createAppContainer(Navigate);</p>