AMO is deprecating jQuery 2

[itskdog]

Email from Mozilla:

jQuery 2.x is no longer maintained and contains vulnerabilities that could lead to security issues in add-ons. Effective immediately, the validation process will warn you if jQuery 2.x is found during the submission of a new version or add-on. After September 1, 2018, no new submissions using jQuery 2.x will be accepted.

We need to adjust CatBlock to use jQuery 3 if we don't already.