Use Pylint instead of pep8 in travis ci

[chemistry-sourabh]

pep8 just checks style conventions whereas pylint also checks for compile issues which is useful before running actual tests.

[naved001]

just read about pylint. Seems like a good idea to have it.

[chemistry-sourabh]

let other @CCI-MOC/bmi-breakers also respond

[sirushtim]

+1

[ravisantoshgudimetla]

+1000 - I just looked at the documentation. Seems it has lot of stuff like code analysis(which can help in refactoring etc).

[naved001]

It would be a good idea to enable one feature of pylint at a time, like how we are doing it in HIL.

https://github.com/CCI-MOC/hil/blob/master/ci/pylint_tests.sh#L8-L17

I think it took 4-5 PRs to enable those checks in pylint.

[naved001]

Looks like we'll be rewriting most of the code, so it would be a good idea to enable pylint from the beginning.