message: Future-proofed modal hand back on ios
  On ios, the onRequestClose can be called when showing modal with pageSheet and dismissed with a swipe. Thought this fix was in already, but it's not working. Adding the check so it skips on ios when the fix lands
diff: import React from 'react';
  +import { Platform } from 'react-native';
  import BackHandlerContext from './BackHandlerContext';
  import createBackHandler from './createBackHandler';
  @@ -6,12 +7,16 @@ class ModalBackHandler extends React.Component<any> {
  private backHandler: any;
  constructor(props) {
  super(props);
  + this.handleBack = this.handleBack.bind(this);
  this.backHandler = createBackHandler();
  }
  + handleBack() {
  + return Platform.OS === "android" && this.backHandler.handleBack();
  + }
  render() {
  return (
  <BackHandlerContext.Provider value={this.backHandler}>
  - {(this.props as any).children(this.backHandler.handleBack)}
  + {(this.props as any).children(this.handleBack)}
  </BackHandlerContext.Provider>
  );
  }
  