Set celerity.minify true in production environments.

Summary: I haven't been able to understand why this isn't set by default in production environments (since it is recommended to do so anyway).

Test Plan: N/A

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D8743