Travis CI failing on python3.7, scipy==0.19.1 #321

PR #320 is failing Travis CI tests because of a conflict generated by the command

conda install scipy==0.19.1 matplotlib

The error message is

UnsatisfiableError: The following specifications were found to be incompatible with each other:
  - pip -> python[version='>=3.6,<3.7.0a0']

All other versions of the test matrix are OK, os presumably this is something specific to using SciPy version 0.19.1 on Python 3.7.