title: react component not updating state
body: <p>When I console log the state it returns undefined but in my react dev tools I can see the resulting array.
  this is the component: </p>
  
  <pre><code>    var Categorias = React.createClass({
    getInitialState: function () {
      return {
        items: []
      };
    },
  
  componentWillMount: function (){
    var  firebaseRef = new Firebase("https://rapifood.firebaseio.com/categorias");
    firebaseRef.on("child_added", function(dataSnapshot) {
      var items= [];
      items.push(dataSnapshot.val());
      this.setState({
        items: items
      });
    }.bind(this));
  },
  
  componentDidMount: function () {
    console.log(this.state.items);
  },
  </code></pre>
  
  <p>What am I doing wrong? </p>