Add require annotate. (#465)

Author: Sachin S Wagh

lib/generators/annotate/templates/auto_annotate_models.rake

@@ -2,6 +2,7 @@
 # NOTE: are sensitive to local FS writes, and besides -- it's just not proper
 # NOTE: to have a dev-mode tool do its thing in production.
 if Rails.env.development?
+  require 'annotate'
   task :set_annotation_options do
     # You can override any of these by setting an environment variable of the
     # same name.