require 'rails/generators' in import_generator.rb

On Rails 4.1 (and I think earlier versions too) the import generator causes an exception when loaded because the `rails/generators` are not required.

> /.../refills-0.0.1/lib/refills/import_generator.rb:2:in `<module:Refills>': uninitialized constant Rails::Generators (NameError)

This [StackOverflow answer](http://stackoverflow.com/a/14884631/1028953) pointed me in the right direction.