bundler_version_with_reason

# File lib/rubygems/bundler_version_finder.rb, line 14
  def self.bundler_version_with_reason
    if v = ENV["BUNDLER_VERSION"]
      return [v, "`$BUNDLER_VERSION`"]
    end
    if v = bundle_update_bundler_version
      return if v == true
      return [v, "`bundle update --bundler`"]
    end
    v, lockfile = lockfile_version
    if v
      return [v, "your #{lockfile}"]
    end
  end