Fix various spelling mistakes

Summary: Minor change, self-explanatory.

Test Plan: Eye-ball it.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9910
Patch: don't complain about reviewers not being specified.
This will break in the future when upstream arc incorporates T4631. Hopefully there will be a better solution by then