Why do I get this watir error in ruby?

My code is very basic.

require 'watir'
require 'watir-webdriver'

browser = Watir::Browser.new :ff
browser.goto "http://www.google.com"

yet the error I get returns :

/Users/.../.rvm/rubies/ruby-2.2.0/lib/ruby/site_ruby/2.2.0/rubygems.rb:1119:in `each': stack level too deep (SystemStackError)

In terminal it also says there are errors in a lot of lib/drivers