Travis on mac

[simontorres]

Trying to get travis working for mac

[coveralls]

Pull Request Test Coverage Report for Build 404

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 8 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.04%) to 55.556%

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Files with Coverage Reduction	New Missed Lines	%
goodman_pipeline/core/check_version.py	1	95.83%
goodman_pipeline/core/core.py	3	66.33%
goodman_pipeline/core/tests/test_check_version.py	4	90.48%

Totals
Change from base Build 392:	0.04%
Covered Lines:	2197
Relevant Lines:	3610

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💛 - Coveralls

[simontorres]

It is working now but I'm not convinced this should be merged, because it is not clear to me yet how to test several versions of python.I'm copying ideas from specutils' setup.