SymPy is not being found on the Travis OSX builds

[moorepants]

$ python test_installation.py

SymPy must be installed for the tutorial

Traceback (most recent call last):

  File "test_installation.py", line 10, in <module>

    if sympy.__version__ != '1.1':

NameError: name 'sympy' is not defined

It seems like it gets installed, but this is failing. Haven't looked deep into it.