In generic_send_email, check if mail object responds to delivery method instead of checking inheritance from ActionMailer (#211)

* Check if mail object responds to delivery method

Instead of checking for an inheritance of ActionMailer::Base,
just see if the conffigure mailer and method respond to the configured
delivery method.

Since both the mailer and the willingniess to automatically send out
messages can be configured, the message should be send if it is
sendable, regardless of which Class the configured mailer inherits
from.

* Add empty mainifest.js to rails_app

Not having a manifest was causing issues running `bundle exec rake`
with sprockets 4.

Author: Plsr

lib/sorcery/model.rb

@@ -206,7 +206,7 @@ def clear_virtual_password
       def generic_send_email(method, mailer)
         config = sorcery_config
         mail = config.send(mailer).send(config.send(method), self)
-        return unless defined?(ActionMailer) && config.send(mailer).is_a?(Class) && config.send(mailer) < ActionMailer::Base
+        return unless mail.respond_to?(config.email_delivery_method)
 
         mail.send(config.email_delivery_method)
       end