Fix pyyaml requirement
Fix pyyaml requirement

The correct python package name is `pyyaml`. Anaconda also provides a `yaml` package, but that seems to provide Linux/Mac-only binaries, rather than python bindings.
andyneff/IPython-notebook-extensions,benvarkey/IPython-notebook-extensions,jbn/IPython-notebook-extensions,juhasch/IPython-notebook-extensions,juhasch/IPython-notebook-extensions,jcb91/IPython-notebook-extensions,ipython-contrib/IPython-notebook-extensions,jcb91/IPython-notebook-extensions,andyneff/IPython-notebook-extensions,andyneff/IPython-notebook-extensions,ipython-contrib/IPython-notebook-extensions,jcb91/IPython-notebook-extensions,benvarkey/IPython-notebook-extensions,benvarkey/IPython-notebook-extensions,jbn/IPython-notebook-extensions,ipython-contrib/IPython-notebook-extensions,juhasch/IPython-notebook-extensions,jbn/IPython-notebook-extensions,andyneff/IPython-notebook-extensions,ipython-contrib/IPython-notebook-extensions,benvarkey/IPython-notebook-extensions,jbn/IPython-notebook-extensions