simplecov 0.14.0 on Ruby Gems

Enhancements

Officially support JRuby 9.1+ going forward (should also work with previous releases). See #547 (ping @PragTob when encountering issues)
Add Channel group to Rails profile, when ActionCable is loaded. See #492 (thanks @BenMorganIO)
Stop extending instances of Array and Hash during merging results avoiding problems frozen results while manually merging results. See #558 (thanks @aroben)

Fix parallel_tests when a thread ends up running no tests. See #533 (thanks @cshaffer)
Skip the :nocov: comments along with the code that they skip. See #551 (thanks @ebiven)
Fix crash when Home environment variable is unset. See #482 (thanks @waldyr)
Make track_files work again when explicitly setting it to nil. See #463 (thanks @craiglittle)
Do not overwrite .last_run.json file when refuse_coverage_drop option is enabled and the coverage has dropped (lead to you being able to just rerun tests and everything was fine). See #553 (thanks @Miloshes)