Support separate color var

[jonallured]

This gem assumes that a project has set their RAILS_ENV in staging and production to different values and that's certainly one way to do it, but another way is to set them both to production to ensure that the app setup doesn't drift. This is how we have convection setup, for example.

So this PR just adds a way to override the reliance on Rails.env with a separate ENV var called CONSOLE_COLOR_ENV.

Note that the git ignore file actually removes the tests from the repo so I was not able to test this change. I guess I could link my local convection to this gem on my machine to ensure it works as expected, but I would love to get some rspec coverage on this project - what do you think @joeyAghion?

[jonallured]

Ok yeah that did work:

# Gemfile
gem 'console_color', path: "../console_color"

jon@juggernaut:~/code/convection(add-published-submissions*)% bundle exec rails console
convection:development>

jon@juggernaut:~/code/convection(add-published-submissions*)% CONSOLE_COLOR_ENV=hahaha bundle exec rails console
convection:hahaha>

[joeyAghion]

I endorse this change! Staging should really run in production mode where possible.