Actually run tests against rubocop master. The matrix contained the gemfile overwrite but it wasn't actually used anywhere. I've also changed it to use the Gemfile.local logic since that was already there.
Moved jruby to the testing matrix. There wasn't much difference between the files, except that jruby didn't run on scheduele previously but I don't think that was intentional.
Remove explicit CI: true. GitHub sets that automatically
Test against the earliest supported RuboCop version. I had to tweak one test that was passing an option unknown to earlier RuboCop versions. That option was renamed, and passing the shorthand avoids deprecation warnings on current versions.
Gemfile.locallogic since that was already there.CI: true. GitHub sets that automatically