Allow Mojave bottles to be used on future versions of MacOS

[fredemmott]

Untested, however as Azure Pipelines doesn't currently support Catalina, we can't natively build for Catalina, so seems better than nothing.

[fredemmott]

Plan is:

• build a nightly (maybe a rebuild)
• find someone with catalina to test
• run HSL unit tests
• if it works, backport to release branches and build; if not , revert