Fix bug in doctest for README
Fix bug in doctest for README

The doctests arefailing sometimes due to unpredictable order of what is
returned by `asserts`.

See below for the problem:
https://travis-ci.org/openworm/PyOpenWorm/builds/66745674#L586-L591

Former-commit-id: 3af0f33d761d850988fa7dce77488101f1cd0f54
hnunner/PyOpenWorm,openworm/PyOpenWorm,openworm/PyOpenWorm,travs/PyOpenWorm,gsarma/PyOpenWorm,kaustubhcs/PyOpenWorm,gsarma/PyOpenWorm