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.
This is picky wording, but do you really mean matrices or just arrays. I try to be careful in my wording around Numpy since I rarely am doing matrix math and in Numpy an array is different from a matrix