PyYAML build errors

[jbarno]

Not sure if this is my (and travis machines issues): ```Best match: PyYAML 5.1b1
Processing PyYAML-5.1b1.tar.gz
Writing /tmp/easy_install-iAsaB7/PyYAML-5.1b1/setup.cfg
Running PyYAML-5.1b1/setup.py -q bdist_egg --dist-dir /tmp/easy_install-iAsaB7/PyYAML-5.1b1/egg-dist-tmp-M6EyYJ
In file included from ext/_yaml.c:591:0:
ext/_yaml.h:6:0: warning: "PyUnicode_FromString" redefined

Might be time for the better yaml lib ruelyaml? 

[jbarno]

was my machine. updaing dependencies fixed this. Verifying the pin change fixes it on travis too,