Bundler ignoring `BUNDLE_WITHOUT`

Whilst investigating why BUNDLE_WITHOUT was not ignoring my development dependencies, I noticed that even when I figured out the problem, bundler was not accepting my input for BUNDLE_WITHOUT.

`BUNDLE_WITHOUT` not working with `development` group

Given the following Gemfile which installs rspec as both a test and development dependency:

Publishing a Ruby Gem to the GitHub Package Registry

When trying to publish a new gem to the GitHub package registry I received the following error:

Installing Ruby 1.9.3 on CentOS 6

The easiest way to do this is to use Software Collections.

Jekyll: Failed to build gem native extension

When trying to install jekyll, I got the following error: mkmf.rb can't find header files for ruby at /usr/lib/ruby/include/ruby.h