The arizona-bootstrap dev dependencies need re-synchronized with the v4-dev branch of upstream bootstrap

[mmunro-ltrr]

Describe the bug
Upstream https://github.com/twbs/bootstrap/tree/v4-dev now includes another set of dev dependency changes, in particular from the pull request twbs/bootstrap#30006 ( I like the phrase in the initial comment “In the past we considered such changes breaking ones.“). For example, there is a move to a new major release version of Jekyll.

To Reproduce
Steps to reproduce the behavior:
View the arizona-bootstrap repository on GitHub: there is now a security warning which does not appear on the upstream repository.
Errors appear in some local development environments.