edits for documentation

Author: yousefhamza

README.md

@@ -44,7 +44,7 @@ import Instabug from'instabug-reactnative';
 class testApp extends Component {
  constructor() {
  super();
- Instabug.startWithToken('YOUR_TOKEN', Instabug.constants.invocationEvent.floatingButton);
+ Instabug.startWithToken('YOUR_TOKEN', Instabug.invocationEvent.floatingButton);
  }
  ...
 }