Using backspace in the editor deletes element even when editing values outside of the canvas area

## What did you do?
When using the editor, the backspace button always deletes the element. Even if you're using the backspace in the form to edit the width, height, etc., the element will still get deleted. This is frustrating as there is also no undo button.

## What did you expect to happen?
If you're editing the values in the form outside of the canvas area using backspace should not delete the element.

## What happened actually?
The element is deleted when using backspace no matter what you're doing.

### Which versions of react-content-loader, and which browser are affected by this issue?
The latest, and Chrome.

If the cursor is outside of the canvas area, like to edit the width or height of the element, using backspace should not also delete the element. Or having an undo button would be highly beneficial.