Updating jquery.lazyloadxt to 0.8.12

Fixes some of the fallout from #2492

Source: https://github.com/ressio/lazy-load-xt/archive/0.8.12.zip
Update string.js to 1.8.0

Fixes remaining fallout from #2492
Merge pull request #2500 from petecooper/master

Fix fallout from #2492 Travis failure