Update jquery.tablesorter.widgets.js

introduced isWebkit var to address issue - https://github.com/Mottie/tablesorter/issues/429
Prevent filter error. Fixes #432
Stop repeated filter widget searches. Fixes #431
Merge pull request #433 from marcinrosinski/master

Update jquery.tablesorter.widgets.js
Merge branch 'master' of github.com:Mottie/tablesorter
revert pull request #433
Remove Bootstrap filter cell background color. Fixes #425
update editable widget docs
editable_columns now accepts a range string. Fixes #435
Add css sticky header widget (beta). See issue #429
Invalid group class now fails silently. Fixes #438
version bump