Deprecate jQuery.isNumeric docs changes

[ShashankaNataraj]

Raising this issue as per the PR checklist. There are docs changes involved with fixing: jquery/jquery#2960

[Schweinepriester]

+1

Mentioned in https://blog.jquery.com/2018/01/19/jquery-3-3-0-a-fragrant-bouquet-of-deprecations-and-is-that-a-new-feature/ but not yet in the docs…