title: Cannot read Property of undeifned Cards material ui
body: <p>I am using cards from material ui in my react project. I am trying to use two functions in my cards, onMouseOver and onMouseOut. But my code is giving me an error saying "Uncaught TypeError: Cannot read property 'onMouseOver' of undefined". Here is an abstract on that part from my code. </p>
  
  <pre><code>class ExpandableCard extends Component {
      constructor(props) {
          super(props);
          this.state = {shadow: 1}
      }
  
      onMouseOver = () =&gt; this.setState({shadow: 3});
  
      onMouseOut = () =&gt; {this.setState({shadow: 1})
      };
  
      render(){
          var Populate = this.props.mediaFiles.map(function (value) {
              return (
              &lt;MuiThemeProvider&gt;
                  &lt;Card key = {value.id}
                        onMouseOver={this.onMouseOver}
                        onMouseOut={this.onMouseOut}
                        zDepth={this.state.shadow}
                  &gt;
  </code></pre>