Fix bug where CC value is ignored on intial parse from commit message

Summary: While I thought this was complicated, there was nothing subtle or
tricky here -- I just misnamed a variable.

Test Plan: Created a revision with default CCs, got CCs instead of nothing.

Reviewers: aran, jungejason, tuomaspelkonen

Reviewed By: aran

CC: aran

Differential Revision: 834