Patient data example update

Aaron and I changed the "Analyzing Patient Data" challenge #2, replacing "Grace Hopper" with other strings relevant to the problem and inverting the order of the assignation to show that we can do this (handy when we need to invert key value pairs). Also, we fixed a typo.
@chendaniely Thanks for your comment, but I don't quite understand the nuts and bolts of how the conversion between ipython notebook and markdown is made and I don't understand where I should put the "! head" you are suggesting. Is that something that is critical to be done for this pull request to be accepted? Or is it something that could be the object of a separate pull request (by someone with more experience than me?)