Fix jQuery deprecation notices (has PR)

[DavidAnderson684]

Running on jQuery 3.5 (and possibly earlier versions) results in plenty of jQuery deprecation notices in your browser console.

PR to update deprecated code: https://github.com/Mottie/tablesorter/pull/1786

N.B. This could potentially affect compatibility with older jQuery versions, so you may wish to make a version bump together with it.