title: Class Binding, Array Syntax issue
body: <p>very new to Vue and seem to be getting on great apart from this little hicup and need abit of direction. I’m working on a hotels app for a travel website that displays hotels on a webpage, I want to toggle hotels based on it’s attributes/ratings via multiple checkboxes.</p>
  
  <p>I’m trying to apply conditional classes based on boolean values within hotel object within my main array. This works when I’m applying the ternary expression within v-bind but when I turn this into a computed it no longer recognises the values within my hotels array. Code &amp; <a href="https://jsfiddle.net/MattPremier/713zysp9/16/" rel="nofollow noreferrer">JSfiddle</a>, any ideas?</p>
  
  <p>WORKING EXAMPLE</p>
  
  <pre><code>&lt;div v-if="" id="hotel-card" class="card" v-bind:class="[hotel.spa ? spaClass : '', hotel.family ? familyClass : '', twoStarClass]" v-for="hotel in filteredList"&gt;
      &lt;img id="hotel-thumbnail" v-bind:src="hotel.img"/&gt;
  
      &lt;p class="hotel-loc"&gt;{{ hotel.loc }}&lt;/p&gt;
      &lt;h3 class="hotel-title"&gt;{{ hotel.title }}&lt;h3&gt;
      &lt;p class="hotel-desc"&gt; {{ hotel.desc }} &lt;/p&gt;
        &lt;p class="hotel-loc"&gt;{{ hotel.star }} Star&lt;/p&gt;
     &lt;a v-bind:href="hotel.link" target="_blank"&gt;&lt;button class="btn-dark"&gt;From £{{hotel.price}}pp &lt;/button&gt;&lt;/a&gt;
  </code></pre>
  
  <p>NOT WORKING</p>
  
  <pre><code>&lt;div v-if="" id="hotel-card" class="card" v-bind:class="classObject" v-for="hotel in filteredList"&gt;
      &lt;img id="hotel-thumbnail" v-bind:src="hotel.img"/&gt;
  
      &lt;p class="hotel-loc"&gt;{{ hotel.loc }}&lt;/p&gt;
      &lt;h3 class="hotel-title"&gt;{{ hotel.title }}&lt;h3&gt;
      &lt;p class="hotel-desc"&gt; {{ hotel.desc }} &lt;/p&gt;
        &lt;p class="hotel-loc"&gt;{{ hotel.star }} Star&lt;/p&gt;
      &lt;a v-bind:href="hotel.link" target="_blank"&gt;&lt;button class="btn-dark"&gt;From £{{hotel.price}}pp &lt;/button&gt;&lt;/a&gt;
  
       &lt;/div&gt;
  
  &lt;script&gt;
  computed: {
   classObject: function () {
   return {
   'spa': hotel.spa,
  'two-star': hotel.star,
  'family': hotel.family,
  }}
  &lt;/script&gt;
  </code></pre>