React to the Smooch trigger related to story mention.

The tipline bot should react to the Smooch trigger that happens when a connected Instagram account is mentioned in a story. This is required in order for the Facebook app to be approved.

Fixes: CV2-3727.

app/models/bot/smooch.rb

@@ -302,7 +302,7 @@ def self.run(body)
       when 'message:delivery:failure'
         self.resend_message(json)
         true
-      when 'conversation:start'
+      when 'conversation:start', 'conversation:referral'
         message = {
           '_id': json['conversation']['_id'],
           authorId: json['appUser']['_id'],