staging repo compatibility for older git versions

Summary:
The --no-verify flag was not added until git 1.8.2. This
flag is used to avoid running local pre-push hooks. This is likely a
rare configuration and is safe to omit the flag on older versions.
Users with local pre-push hooks and older git version may need to
adjust their workfow.

fixes T9310

Test Plan:

• Ran arc diff with my real git 1.7.10.4 and succeeded with STAGING PUSHED.
• Edited getGitVersion to be > 1.8.2 and pushed again. Got STAGING FAILED because error: unknown option.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: joshuaspence, epriestley

Maniphest Tasks: T9310

Differential Revision: https://secure.phabricator.com/D14033