Actually send an email when a proposition is created

app/models/proposition.rb

@@ -1,11 +1,11 @@
 class Proposition < ActiveRecord::Base
   belongs_to :proposer, class_name: 'User'
   belongs_to :proposable, polymorphic: true
-
   enum status: [:undecided, :approved, :rejected, :backup]
-
   delegate :proposable_title, :proposable_type, :proposable_description, to: :proposable
 
+  after_create :send_creation_notification
+
   def send_creation_notification
     PropositionMailer.new_proposition_notification(self).deliver_later
   end