title: React-Dropzone image preview not showing
body: <p>Using react-dropzone (<a href="https://www.npmjs.com/package/react-dropzone" rel="noreferrer">https://www.npmjs.com/package/react-dropzone</a>) and getting files logging to the console, but can't get image preview to populate on state change. Any idea what I'm doing wrong?</p>
  
  <pre><code>export default class JoinForm extends Component {
      constructor(props) {
      super(props)
          this.state = {
              imageFiles: []
      }
  }
  
  onDrop(imageFiles) {
      this.setState({
          imageFiles: imageFiles
      })
      console.log(imageFiles)  
  }
  
  render() {
  
      return(
          &lt;form className='join-form' ref='joinForm' autoComplete='off'&gt;
              &lt;Dropzone
                  onDrop={this.onDrop}
                  className='dropzone'
                  activeClassName='active-dropzone'
                  multiple={false}&gt;
        &lt;div&gt;Drag and drop or click to select a 550x550px file to upload.&lt;/div&gt;
      &lt;/Dropzone&gt;
  
              {this.state.imageFiles.length &gt; 0 ? &lt;div&gt;
      &lt;h2&gt;Uploading {this.state.imageFiles.length} files...&lt;/h2&gt;
      &lt;div&gt;{this.state.imageFiles.map((file) =&gt; &lt;img src={file.preview} /&gt; )}&lt;/div&gt;
      &lt;/div&gt; : null}
          &lt;/form&gt;
      )
  }
  </code></pre>
  
  <p>};</p>