removed local reference for active admin
removed local reference for active admin

This plugin will require some small changes to ActiveAdmin.

https://github.com/gregbell/active_admin/pull/1752

randym/activeadmin-axlsx,owhat/activeadmin-axlsx,ivannovosad/activeadmin-axlsx,hyperoslo/activeadmin-axlsx,antob/activeadmin-axlsx,toothfairy/activeadmin-axlsx,moscn/activeadmin-axlsx,studentcompetitions/activeadmin-axlsx