[keen-io] Pull Request #18: update integration to use keen-tracking v2 and parsers

_Migrated from [#18](https://github.com/segment-integrations/analytics.js-integration-keen-io/pull/18) by @adamkasprowicz_

Hi Devs!
This PR updates Segment integration with Keen.IO
Please note, there are some breaking changes, so publishing this package on NPM requires Major version update (to 3.0.0)
Fixes: #17 , #5 , #1
Thanks

@tysonmote