add travis configuration file including coverage

[simbabque]

To turn this on, create an account at https://travis-ci.org/ and link it to your github account. Then enable this repository. If you want test coverage reports too, do the same with https://coveralls.io/.

This is my entry to the Pull Request Challenge 2017 for September.

[briandfoy]

Travis took back its promise on open source stuff, but I'm working on this module in briandfoy/cpan-mini-inject and will set up GitHub Actions and Appveyor.

I can't close this issue because I'm not part of this repo, although PAUSE considers me the module owner (but not author!).