fix for generators required

Author: piratechicken

lib/knock/engine.rb

@@ -1,6 +1,12 @@
 module Knock
   class Engine < ::Rails::Engine
     config.eager_load_paths += Dir["#{config.root}/lib/**/"]
+    # https://github.com/nsarno/knock/issues/156
+    if ::Rails.const_defined? 'Generators'
+      config.eager_load_paths += Dir["#{config.root}/lib/**/"]
+    else
+      require_relative './authenticable'
+    end
     isolate_namespace Knock
   end
 end