Fix duplicate gem warning in Gemfile

Group `:development` and `:test` both had `rr` and `rake` pegged at the same
version, and Bundler was complaining.

This commit breaks them out into their own block
Merge branch 'gemfile_fix'

* gemfile_fix:
  Fix duplicate gem warning in Gemfile
Never use the PGBACKUPS_URL from the environment

It's not clear from the history why this was introduced in the first
place, but the only conceivable use I can think of is testing against
a staging version of PGBackups, but that can easily be done by
actually adding the staging add-on to an app.
Merge pull request #1001 from deafbybeheading/no-pgbackups-url-from-env

Never use the PGBACKUPS_URL from the environment
An authentication failure from an API key should exit 1.
Merge pull request #716 from keithpitt/heroku-api-key-auth-exit-1

An authentication failure from an API key should exit 1.
Add optional number to releases command

Add a `-n`, `--num` flag to the `releases` index command, to specify the number
of releases to be shown.

Implements #494
Merge pull request #1012 from catsby/release_number

Add optional number to releases command