Use active :dev profile in project instead of LEIN_NO_DEV

[jcrossley3]

How do you feel about querying the project metadata for :dev in the :active-profiles seq to indicate "development mode"? Something along these lines in ring.server.leiningen/serve, maybe?

(with-env {"LEIN_NO_DEV" 
           (or (System/getenv "LEIN_NO_DEV")
               (->> project meta :active-profiles (not-any? #{:dev})))} ...)

If it makes sense to you, I can submit a PR.