Update jquery-timeago to 1.3.1.

Source code retrieved from v1.3.1 tag:
https://github.com/rmm5t/jquery-timeago/releases/tag/v1.3.1

Minified version created with uglifyjs --comments @preserve.
Merge pull request #2526 from smola/jquery-timeago-1.3.1

Update jquery-timeago to 1.3.1.