Lock tablesorter to version 2.28.6
Lock tablesorter to version 2.28.6

Fix for #688

alexweissman/UserFrosting,alexweissman/UserFrosting,alexweissman/UserFrosting,alexweissman/UserFrosting,splitt3r/UserFrosting,splitt3r/UserFrosting,splitt3r/UserFrosting