Fixes multiple newrelic deploy notifications

The use of `on roles(:app)` here is unnecessary. The body of this block doesn't actually include any `execute`, `upload`, or `capture` commands, and thus doesn't actually ever execute on the remote servers. What happens instead is for every `:app` server you have, you locally notify NewRelic of the deployment, resulting in N-1 duplicate notifications for N app servers.

I simply changed this `run_locally` which is intended for locally executing code. This way you get at most one deployment notification.