Update JRuby version to 9.2.8.0 + remove EOL Ruby 2.2

Fix after_commit for Rails 6

`gem update --system` fails with Ruby 2.2.

Activerecord 6 support

The versions we were running against were bumped, so we needed to update
which versions were being excluded as they were stale.

Rails master (soon to be 6.0.0) doesn't support versions before Ruby
2.5.

These versions of rails enforce this version constraint when loading the
sqlite adapter so we need to make sure that we always use a compatible
version.

Older versions of activerecord require sqlite ~> 1.3.6, but not in the
gemfile, the constraint is enforced when you load the adapter.

This allows us toe specify in the environment the version of the gem
we'd like to run against.

We are trying to test our application on rails 6.0.0.alpha but we can't install this because of the version lock
Probably this will be helpful that we can try and report any issues with edge rails

Add Ruby 2.6 to Travis CI.

Fix typo (`6.2.0` -> `5.2.0`)

Version 2.4.1

Improvements to rails 5.2 patches

Monkeypatch activerecord relations to work with rails >=5.2.0rc2

Test new ruby versions