Youtube in React: wire up comments reducer to root reducer

index.js

import apiReducer from './api';
import {combineReducers} from 'redux';
import videosReducer from './videos'
import channelsReducer from './channels';
import commentsReducer from './comments';

export default combineReducers({
  api: apiReducer,
  videos: videosReducer,
  channels: channelsReducer,
  comments: commentsReducer,
});