Update CI pipeline

[mathematicalmichael]

trying a few things, including switching to nosetests syntax, addressing paulcon#53 and to be added onto paulcon#52

EDIT: hopefully able to switch from nosetests to pytest without a hitch.

[mathematicalmichael]

test.py can be removed in favor of setting matplotlib settings with command-line in travis:
matplotlib.use('agg') can be done differently, though I understand why this route was chosen.

export MPLBACKEND="Agg"

[mathematicalmichael]

reminder to be doing a squash merge to keep this clean. lot of trial/error that there's no use keeping a history of.

[mathematicalmichael]

okay let's try nosetests first then deal with pytest later...
looks like these tests weren't written to reflect module names, which is pytests's assumption