feat: travis testing

[Freyert]

unit tests run on PRs.

After looking at the org.cellocad.MIT.dnacompiler.Permute class for 15 or so minutes I couldn't really make heads or tales of it so I just wrote a pretty lame unit test that just works (Java is not my native language ;p). If someone can give me pointers on how to make the unit test more useful I would like that :).

If you've never heard of Travis, it's the bees knees for many reasons:

1. Anytime someone makes a PR it will run your unit testing suite to verify the PR does not contribute any regressions in the code.
2. Simple to verify version compatibility as desired in Cello doesn't work well with Java 8 #29.
3. Free for open source projects, and used by loads.

[Freyert]

Also, your code base, at least the really interesting bits, seem to all be functions rather than methods with side effects. Therefore, unit testing will give you significant gains in terms of project velocity and quality.

[Freyert]

You will have to create a Travis account for your organization though.
https://docs.travis-ci.com/user/getting-started/

[Freyert]

@bder who is maintaining this project?

[Freyert]

@PrashantVaidyanathan @tim-tx any interest in this PR?

[PrashantVaidyanathan]

@Freyert Apologies for the late reply. We do plan to have some sort of CI (and Travis is a top contender for this). We are currently restructuring some of our code. So we might accept this PR in a couple of days.

[Freyert]

@PrashantVaidyanathan great :) can't wait to see it. This is a very exciting project. I'd love to help out any way I could.