Grammar fix.
chapter 3 small changes
Merge pull request #98 from gbenmartin/master

Minor spelling/grammar in chapter 2
Merge pull request #97 from pushmatrix/patch-1

Grammar fix.
Merge pull request #100 from psinger/master

Spelling / Grammar chapter 3
fixing issue #99
Merge branch 'master' of github.com:CamDavidsonPilon/Probabilistic-Programming-and-Bayesian-Methods-for-Hackers
adding ABtestingpy