#390 added workarounds to not run gem update --system on those old versions. However, looking at git blame, it looks like gem update --system was added a long time ago in 2bd6ebe. In #346, 43f01f4 mentions that it shouldn't be needed and removes it but then brings it back in cbdea2a (without comment, even though the previous CI run passed without it).
I have tried removing it again, and it does not seem to be required now --- both JRuby and MRI builds seem OK with just using the default rubygems version. So, in this PR I have removed it.
I was instead going drop the EOL versions from travis, but in the gemspec we are still requiring ruby version >= 1.9.2, so I feel like we should continue testing on older versions until we bump that requirement.
I found the discussion around #254 / #256, and it seems several users and contributors are of the opinion that dropping 1.9 from the test matrix, which was done because rubocop no longer supported 1.9, should have been a major version bump.
For the moment, with gem update --system removed, the old ruby versions are not causing any problems, so I have left them in. If we want to upgrade rubocop again, which I think would be helpful for supporting frozen string literals (#390 / #374), then we may need to drop them or remove rubocop as a dev dependency (it could e.g. go into the Gemfile in a group that would only be installed for some rubies, but this seems like a lot of complexity to support very old ruby versions).
I reverted #375 - the underlying JRuby bug now seems to be fixed, so we don't need to ignore it.
The other source of spurious CI problems is coveralls: sometimes the coverage numbers drop even though no code has changed. I think we may need to enable parallel build support: http://docs.coveralls.io/parallel-build-webhook --- otherwise, I think there is a race on which build finishes last (usually one of the JRuby builds). I'm not sure about this, but I would like to try it out.
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