Empty elements marked with data-sample attr gets extra whitespice inside

[mlewand]

If you add an element like <script data-sample="1" src="https://code.jquery.com/jquery-2.2.3.min.js"> to the sample, it will get an unnecesary whitespaces when getting the code listing.

I'd expect it simply to preserve original whitespace.

This issue originates from #183.