Fixes #41 If a user is using certain gems (ActiveRecord, ActionMailer, etc) without the rails gem, in a standalone application, they encounter a situation where the Rails module is defined but doesn't have a version method, so improve the check before adding Rails.version to the headers.
Fixes #41 If a user is using certain gems (ActiveRecord, ActionMailer, etc) without the rails gem, in a standalone application, they encounter a situation where the Rails module is defined but doesn't have a version method, so improve the check before adding Rails.version to the headers.