title: Vuex Mutation return last inserted
body: <p>I want to return a value from mutation to action.
  I this case, I want the last inserted object :</p>
  
  <p>In my mutation, work fine :</p>
  
  <pre><code>mutations: {
    insert(state, item) {
      const guid = Math.floor(Math.random() * 6) + 1; // any sense, just example
      item.guid = guid;
      state.data.push(item);
      return guid;
    },
  },
  </code></pre>
  
  <p>In my action, work fine for the call, not for the return :</p>
  
  <pre><code>actions: {
    insert ({ commit }, data) {
      return new Promise((resolve) =&gt; {
        const guid = commit('insert', event);
        resolve(guid); // resolve undefined
      });
    },
  },
  </code></pre>
  
  <p>There is a way to return the guid ?
  I need it to emit after with my component...</p>
  
  <p>Thanks</p>