Fix restore notifications from admins page

The restore feature was not working properly. When pushed, the button
was removing the notification from the admins panel, but it was not
restoring in the proposal.

I added an `after_restore` function (that I missed in the first PR)
so that the notification is unmarked as moderated.

app/models/proposal_notification.rb

@@ -45,6 +45,10 @@ class ProposalNotification < ActiveRecord::Base
     ignored_at.present?
   end
 
+  def after_restore
+    update(moderated: false)
+  end
+
   private
 
   def set_author

spec/features/admin/proposal_notifications_spec.rb

@@ -25,6 +25,7 @@ feature 'Admin proposal notifications' do
 
     expect(proposal_notification.reload).not_to be_hidden
     expect(proposal_notification).to be_ignored
+    expect(proposal_notification).not_to be_moderated
   end
 
   scenario 'Confirm hide' do