title: Using new Date() with v-date-picker doesn't work
body: <p>I'm trying to follow <a href="https://www.youtube.com/watch?v=mhK761NH5EA&amp;list=PL55RiY5tL51qxUbODJG9cgrsVd7ZHbPrt&amp;index=11" rel="noreferrer">this video</a> using Vue and Vuetify to apply the current date with <code>v-model</code> to the date picker component <code>v-date-picker</code> using the data value <code>date</code> that's initially being set with <code>new Date()</code>.</p>
  
  <p>This is a simplified structure of my project:</p>
  
  <p><strong>JS</strong></p>
  
  <pre><code>new Vue({
    el:"#app",
    data: {
      date: new Date(),
      time: new Date()
    }
  })
  </code></pre>
  
  <p><strong>Template</strong></p>
  
  <pre><code>&lt;div id="app"&gt;
    &lt;v-date-picker v-model="date"&gt;&lt;/v-date-picker&gt;
      {{ date }}
    &lt;v-time-picker v-model="time"&gt;&lt;/v-time-picker&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><strong>And here's a <a href="https://codepen.io/anon/pen/MrdBqO" rel="noreferrer">CodePen</a></strong>. Unfortunately I couldn't get the Vuetify CSS to work with the CodePen, but if you open up the console, you'll see that I get errors in the <code>v-date-picker</code> when trying to use <code>new Date()</code> with the <code>v-model</code> directive. Also the date picker isn't rendering. The <code>v-time-picker</code> however works fine.</p>
  
  <p>On my local setup I've created a Vue project with the vue-cli. Here's the error I'm getting there:</p>
  
  <blockquote>
    <p>[Vue warn]: Error in created hook: "TypeError: dateString.split is not
    a function"</p>
    
    <p>found in</p>
    
    <p>---> 
            at src/components/Meetup/CreateMeetup.vue
             
                at src/App.vue
                 </p>
  </blockquote>
  
  <p>I'm doing exactly as in the tutorial I'm following, so I don't know if this is a bug with the latest version of either Vue or Vuetify? Or am I missing something?</p>