Fixes console error when saving canvas to PNG
Fixes console error when saving canvas to PNG

When saving the canvas to PNG, the temporary 'a' element is added to `document.body` so that FireFox will actually register the click() event.  However, the element was being removed from `document` - throwing an error.  This fixes it by correctly removing it from `document.body` instead.
xSke/Pxls,xSke/Pxls,xSke/Pxls,xSke/Pxls