RubyGems 1.8.20+
RubyGems 1.8.20 and adds the skip_validation parameter, so that's when we start passing it through.
# File bundler/rubygems_integration.rb, line 719
def build(spec, skip_validation = false)
require "rubygems/builder"
Gem::Builder.new(spec).build(skip_validation)
end