Fix for old browsers without String.trim

Example: https://bugzilla.wikimedia.org/show_bug.cgi?id=62072 affected
MobileFrontend's "last modified" view on Kindle 3.4 browser

Already submitted in MediaWiki core as https://gerrit.wikimedia.org/r/#/c/116159/
Merge pull request #10 from brion/bug62072

Fix for old browsers without String.trim