fix: Detect Rails via Rails::Railtie

Author: kgilpin

lib/appmap.rb

@@ -57,7 +57,7 @@
     end
   end.enable
 
-  if defined?(::Rails)
+  if defined?(::Rails::Railtie)
     require 'appmap/railtie'
   end
 

lib/appmap/detect_enabled.rb

@@ -104,7 +104,7 @@ def recording_method_enabled?
     end
 
     def rails_env
-      return Rails.env if defined?(Rails)
+      return Rails.env if defined?(::Rails::Railtie)
 
       return ENV['RAILS_ENV']
     end