Revert "change rails server to puma"

This reverts commit e8e5fed83131722c386b9a085b6fc2aa87eeaf86.

Conflicts:
	Gemfile
	Gemfile.lock

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Add Heroku-recommended Unicorn configuration

Signed-off-by: Alex Coles <alex@alexbcoles.com>