[Docs] Minor typo fixes

Author: Nicholas Chammas <nicholas.chammas@gmail.com>

Closes #3772 from nchammas/patch-1 and squashes the following commits:

b7d9083 [Nicholas Chammas] [Docs] Minor typo fixes

(cherry picked from commit 0e532ccb2b282ea5f7b818e67d521dc44d94c951)
Signed-off-by: Patrick Wendell <pwendell@gmail.com>