How do I prevent my "production" group from being called when running in my Rails development enviornment?

Im using Rails 4.2.7 on Mac OS X (El Capitan). I have this at the end of my Gemfile (for my production environment). I have no other references to puma in my Gmefile …

group :production do

  gem 'pg'

  gem 'unicorn'

  gem 'puma'

end

but when I attempt to start my Rails server on my development machine (my Mac), it is attempting to start up Puma …

localhost:networkingproject localuser$ rails s -b 127.0.0.1

=> Booting Puma

=> Rails 4.2.7.1 application starting in development on http://127.0.0.1:3000

=> Run `rails server -h` for more startup options

=> Ctrl-C to shutdown server

[93431] Puma starting in cluster mode...

[93431] * Version 3.6.0 (ruby 2.3.0-p0), codename: Sleepy Sunday Serenity

[93431] * Min threads: 1, max threads: 6

[93431] * Environment: development

[93431] * Process workers: 1

[93431] * Phased restart available

[93431] * Listening on tcp://127.0.0.1:3000

[93431] Use Ctrl-C to stop

localhost:networkingproject localuser$

I don’t have a RAILS_ENV set. The below echoes nothing …

localhost:networkingproject localuser$ echo $RAILS_ENV

How do I make Rails run without Puma (just normally) in my development (Mac) environment?

Edit: Output in response to suggestion given …

localhost:networkingproject localuser$ rails s -b 127.0.0.1

Could not find gem 'puma' in any of the gem sources listed in your Gemfile or available on this machine.

Run `bundle install` to install missing gems.