title: ractivejs.push() returning object.keys error in IE11
body: <p>I have an issue that I can't seem to figure out. I'm using ractiveJS for a DNS management system I'm building. </p>
  
  <p>I'm trying to add a new record to the end of the existing records. I'm using <code>ractive.get('A')</code> to retrieve the current records. I'm then building a new object</p>
  
  <pre><code>var thisRecord = {};
  thisRecord.hostname = "hostname";
  thisRecord.ip = "123.123.123.123";
  </code></pre>
  
  <p>I'm then using <code>records.push(thisRecord);</code> to add it to ractiveJS. In Chrome, Firefox and Safari, this works fine, in IE11, I'm getting the following error coming back.</p>
  
  <p><a href="https://i.stack.imgur.com/Wi9Py.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Wi9Py.png" alt="IE11 Ractive JS Error"></a></p>
  
  <p>Just a note. Even though it's in file auth.js, that file is just a compressed file with a few other files within. The affected line seems to be in RactiveJS and this is the line</p>
  
  <pre><code>return n.isRoot?o=[].concat(Object.keys(t.viewmodel.data),Object.keys(t.viewmodel.mappings),Object.keys(t.viewmodel.computations)):(i=t.viewmodel.wrapped[n.str],r=i?i.get():t.viewmodel.get(n),o=r?Object.keys(r):null),o&amp;&amp;o.forEach(function(t){"_ractive"===t&amp;&amp;s(r)||e.push(n.join(t))}),e
  </code></pre>
  
  <p>Any ideas would be appreciated!</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>I've found out this issue is only in Ractive 0.7.3, the behaviour works as expected in &lt; 0.7.3 and in Ractive 0.8.5, pushing an object into Ractive as above doesn't update the model at all.</p>