Ci update

[Kilo59]

Changes

• now tracking test coverage
  • using pytest with pytest-cov and coverage
  • calling coveralls at end of pipeline to upload coverage report to coveralls.io. You will need to setup a free coveralls account and "turn on" https://coveralls.io/github/aboSamoor/polyglot.
• Adding Python 3.7 to travis
• Allowing failures for Python 3.4 and 3.5
• Adding dev-requirments.txt
• Increasing speed of CI by making better use of travis cache by caching pip dependencies and adding apt dependencies to a separate before_install step.

Questions

I began creating some parameterized tests using examples in the quickstart but they are failing.
I've temporarily marked as "expected to fail" with pytest so that the CI passes.

Am I doing something wrong or is there something missing from the quickstart?