title: redux reducer not updating state
body: <p>I am new to Redux, and reading through the documentation while I try to make a basic to do list.</p>
  
  <p>I can't seem to get my reducer to add an item to the list. The correct action creator is firing, I think there is perhaps something in my <code>Object.assign</code> statement that I am not understanding. Below is my <code>store.js</code> file.</p>
  
  <pre><code>const defaultState = {
      todos:[
    {
      text: 'walk gilbert'
    },
    {
      text: 'cook dinner'
    },
    {
      text: 'clean bathroom'
    }
   ]
  }
  
  function todos(state = defaultState) {
    return state;
  }
  
  function modifyList(state = defaultState, action) {
    switch(action.type) {
      case 'ADD_TODO':
      return Object.assign({}, state, {
          todos: [
            ...state.todos,
          {
              text: action.text,
          }
        ]
      })
  
    default:
      return state;
   }
  }
  
  const rootReducer = combineReducers({todos, modifyList})
  
  const store = createStore(rootReducer, defaultState);
  
  export default store;
  </code></pre>
  
  <p>Thanks!</p>