title: Issue with React Redux array.push
body: <p>I'm having an issue where when I try to update an array in the store by using .push(newvalue). When I push the new value the state is updated from an array to being the value of the length of the array. </p>
  
  <p>State before update: ['asd', 'sdf', 'wer']</p>
  
  <p>State after: 4</p>
  
  <p>action: </p>
  
  <pre><code>export function updateLocalCompliments(newCompliment) {
    return ({
      type: LOCAL_COMPLIMENT,
      payload: newCompliment
    })
  }
  </code></pre>
  
  <p>reducer: (state.compliments is the actual array)</p>
  
  <pre><code>const INITIAL_STATE = {
    compliments: []
  }
  
  function compliments(state=INITIAL_STATE, action) {
        switch (action.type) {
          case LOCAL_COMPLIMENT:
            return (
              Object.assign({}, state, {
                compliments: state.compliments.push(action.payload)
              })
            )
          default:
            return state;
        }
      }
  </code></pre>