Upgrade jQuery to 3.x

[tqnguyen9]

Exhibitor currently ships with jQuery 1.7.1.

At the time of writing, jQuery 1.7.1 has several vulnerabilities. These are ones I found, but there may be more.

https://nvd.nist.gov/vuln/detail/CVE-2015-9251
https://nvd.nist.gov/vuln/detail/CVE-2019-11358

Upgrading jQuery to the latest version (3.4.1 at the time of writing) would eliminate the threat of vulnerabilities from customers.