Require active_support before core_ext to fix uninitialized constant.

Fixes travis error with linux_admin:
https://travis-ci.org/ManageIQ/linux_admin/builds/29519678

This is a known issue with activesupport and travis:
https://github.com/rails/rails/issues/14664

See also:
https://github.com/ManageIQ/polisher/commit/c899d500502a57582a906dfa20cc6cf343c09265