Update drawer-based-navigation.md

Author: brentvatne

docs/drawer-based-navigation.md

@@ -85,9 +85,9 @@ this.props.navigation.dispatch(DrawerActions.closeDrawer());
 this.props.navigation.dispatch(DrawerActions.toggleDrawer());
 ```
 
-If you would like to determine if drawer is open or closed, you can follow:
+If you would like to determine if drawer is open or closed, you can do the following:
 
 ```js
 const parent = this.props.navigation.dangerouslyGetParent();
 const isDrawerOpen = parent && parent.state && parent.state.isDrawerOpen;
-```
+```