title: Vue md-input with Vuex updating only in one direction
body: <p>I have a Vue app with an input element bound to a  like this:</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;template&gt;
     &lt;input v-model="this.$store.state.myvalue"/&gt;
  &lt;/template&gt;
  </code></pre>
  
  <p>and VueX <code>store/index.js</code>:</p>
  
  <pre class="lang-js prettyprint-override"><code>import Vue from "vue";
  import Vuex from "vuex";
  
  Vue.use(Vuex);
  
  export default new Vuex.Store({
    state: {
      myvalue: null
    },
    mutations: {},
    actions: {},
    modules: {}
  });
  </code></pre>
  
  <p>When I modify <code>myvalue</code> with Vue devtools, the input's value changes too, but when I change the value in the input field, the state variable does not change. What am I doing wrong? I'm new to VueX.</p>