Update html10n.js

This updates html10n.js to the latest version overtaking the revamped plural macro, which finally allows the guys on twn to correctly translate some of the potentially more complex messages (Have a look at `timeslider.unnamedauthors` for example)

(Addresses [this twn issue](https://translatewiki.net/wiki/Thread:Support/About_EtherpadLite:Timeslider.unnamedauthor/en_and_EtherpadLite:Timeslider.unnamedauthors/en))