DropEvent.reject()

[taye]

<div class="container" data-color="red"></div>
<div class="container" data-color="green"></div>

<div class="draggable" data-color="red">Item 1</div>
<div class="draggable" data-color="blue">Item 2</div>
<div class="draggable" data-color="green">Item 3</div>

<script>
interact('.container')
  .dropzone({
    accept: '.draggable',
  })
  .on('dragenter', event => {
      const dropzoneElement = event.target;
      const draggableElement = event.relatedTarget;

      if (draggableElement.dataset.color !== dropzoneElement.dataset.color) {
        event.reject();
      }
    })
  .on('drop', event => {
    console.log('dropped');
  });
</script>

• tests
• docs

Close #552