chore(travis): add a new job that runs ci-checks

Previously, ddescribe, merge-conflicts, jshint, and jscs would run
after unit & e2e tests ran. The order was orginally changed as part of
https://github.com/angular/angular.js/pull/9792.

While the logic is sound that style errors shouldn't block tests from
running, ddescribe should always run. This was not guaraneteed; when
Travis exits with a warning after some browsers have run, ddescribe
doesn't get run and it doesn't become apparent that not
all tests have run.

Additionally, a separate job clearly separates style from test errors,
which e.g. means you can open a PR that includes an iit to speed up
the job, and see immediately if the test passes, because the ddescribe
error is in another job.