If a container has non-element child nodes (e.g. comment nodes), sometimes they arenn't returned to the same order after calling drake.cancel().

This CodePen shows hopefully demonstrates the issue very clearly on Dragula 3.7.2: https://codepen.io/anon/pen/ZrXJwd/

The fix seems to be pretty simple. I think I'll creating a PR right away. Please let me know if you recognize this as an issue that needs to be addressed. Comment nodes are used by some SPA frameworks (such as Angular and Aurelia, maybe others) and their placement is relevant to the proper functioning of the SPA, so I think this needs to be addressed (see #302).