Spinach builds failing but marked as successful

NOTE: This is an issue with Spinach, not CI, as far as I can tell.

While working on the Rails 5 MR (!5555 (closed)) I've noticed that the Spinach builds will sometimes error out but then return an exit value that makes CI think they've passed. I don't know if we can fix this on our end, or if this is something that'd need to be fixed with a patch to the gem itself (good luck with that). If this is something we can fix easily, we should. Otherwise it's probably not enough of a problem to be concerning (Rspec usually has tests that would also throw errors if Spinach were, and they'd fail properly).

I haven't seen it effect any other MRs, but I figured I'd report it before it has the chance to bite us later on.

Examples: