MJML binary attempting to make Internet connection every time it's run?

[denny]

Tests of MJML mailers (Forms, Newsletters, etc) throw this warning when run offline:
"Mjml: warning You don't appear to have an internet connection. Try the --offline flag to use the cache for registry queries."

The Newsletter plugin tests tend to top the 'slowest tests' list, which could be related - network delays rather than slow or complicated code.

[denny]

Did a bit of digging into this and running the mjml commands on the command line doesn't trigger the same warning, so it would appear to be something about how the Ruby gem uses it? Need to create an isolated test case next, I think.