Fix for trivial assertion noticed by Py3.4 SyntaxError.
Fix for trivial assertion noticed by Py3.4 SyntaxError.

ihincks/python-qinfer,QInfer/python-qinfer,whitewhim2718/python-qinfer,Alan-Robertson/python-qinfer,MichalKononenko/python-qinfer,csferrie/python-qinfer