title: ractive array is changing, but not computed value
body: <p>I use an array of objects as data for my ractive component (received from a PouchDB) which needs filtering inside ractive for the proper output. But anything I tried - even if the data - referred to as "docs" is changed correctly, the filtered aka computed values stay the same.</p>
  
  <p>I tried with method:</p>
  
  <pre><code> new Ractive({
          el: '#container',
          template: Listing,
          magic: true,
          modifyArrays: true,
          data: {docs},
          computed: {
              List: function(){
                  let tempList = [];
                  for(var i = 0; i &lt; docs.length; i++) {
                      if (docs[i].specificValue == otherValue)  {
                          let newValue = docs[i];
                          tempList.push(newValue);
                      }
                  }
                  return tempList;
                  }
              }
      });
  </code></pre>
  
  <p>with a helper object </p>
  
  <pre><code>Ractive.defaults.data.helper = function () {
          for (var i = 0; i &lt; docs.length; i++) {
              if (docs[i].specificValue == otherValue) {
                  return docs[i].whatever ;
              }
          }
      }
   new Ractive({
          el: '#container',
          template: '{{helper()}}',
          magic: true,
          modifyArrays: true,
          data: {List: docs}
      });
  </code></pre>
  
  <p>and a data function as described in <a href="https://stackoverflow.com/questions/25582912/ractive-computed-property">Ractive computed property</a></p>
  
  <p>But nothing worked the way expected. When I use docs directly the binding works as expected.</p>
  
  <p>PS: the code may look a bit awkward because I just copied and simplified.</p>