Fails to install itermocil-PyYaml on initial install

[joelpierre]

The link to PyYAML-3.11.tar.gz is wrong. Currently it is:

https://pypi.python.org/packages/source/P/PyYAML/PyYAML-3.11.tar.gz

but needs to be...

https://pyyaml.org/download/pyyaml/PyYAML-3.11.tar.gz