Tests are broken with Ruby 2.2.4

$ bundle exec rspec 2>&1 | head
/Volumes/GitLab.com/gitlab-development-kit/gitlab-shell/lib/gitlab_init.rb:1: warning: already initialized constant ROOT_PATH
/Volumes/GitLab.com/gitlab-development-kit/gitlab-shell/spec/spec_helper.rb:1: warning: previous definition of ROOT_PATH was here
[2016-02-09 16:59:37] INFO  WEBrick 1.3.1
[2016-02-09 16:59:37] INFO  ruby 2.2.4 (2015-12-16) [x86_64-darwin15]
[2016-02-09 16:59:37] INFO  HTTPUNIXServer#start: pid=3307 port=80
[2016-02-09 16:59:37] ERROR NoMethodError: undefined method `[]' for nil:NilClass
	/Users/jacobvosmaer/.rubies/2.2.4/lib/ruby/2.2.0/webrick/server.rb:174:in `block in start'
[2016-02-09 16:59:37] ERROR NoMethodError: undefined method `[]' for nil:NilClass
	/Users/jacobvosmaer/.rubies/2.2.4/lib/ruby/2.2.0/webrick/server.rb:174:in `block in start'
[2016-02-09 16:59:37] ERROR NoMethodError: undefined method `[]' for nil:NilClass

(It prints many many times the same error, that is why I put head there.)

cc @jameslopez