thoughtbot/suspenders — pull request #179 by pbrisbin (2013-05-28 21:01:58+00:00)
Title: Fix mailer configuration

default_url_option should be plural, default_url_options

http://api.rubyonrails.org/classes/ActionMailer/Base.html#label-Generating+URLs

I can't find mention of a singular form of this setting/method in any
version of rails.