Minor fixes to lesson 3

-h2 → h1
-b → strong

Note:
It's likely also worth updating the gist at: https://gist.github.com/despo/7328342 to have the adjusted starting styles.
Using **body** instead off __*__ means that the students don't come across another new concept.
Also, I would discourage use of the star selector because of performance issues and unexpected results.