Loosen dependency on delayed job

* Interface is compatible with dj 3.0, so let's allow them to use it
* I'm not convinced the particular version of DJ AR is important, so
  remove this constraint
Merge pull request #3 from iamvery/dj3

delayed_job 3.x
Merge pull request #4 from iamvery/travis

Add CI to project
Add gemfiles for dj 3.x and 4.x for travis
Allow delayed job 3 tests to fail

* Until we can get them passing...
Explicitly require lib from test file
Simplify db setup for tests

* Rather than having a skeleton Rails app, this just creates a table to
  back the Delayed::Job model. Just enough to keep tests green :+1:
Remove unneeded "skeleton" rails app

* No longer needed! :boom:
Remove allowable failures

* DJ 3.x CI fixed :+1: