Fix tests on ActiveSupport v4.2.x
Fix tests on ActiveSupport v4.2.x

* Remove use of `Kernel#capture` to find RSpec deprecation warnings
  because it has has been deprecated.
* Add `require "active_support"` to setup auto-loading.

Closes #252.

demiazz/pundit,elabs/pundit,idlweb/pundit,engineyard/pundit,yatmsu/pundit,ram-krishan/pundit,beanieboi/pundit,jkgold/pundit,luisdaher/pundit,jackjennings/pundit,AlexVPopov/pundit,maxcal/pundit,olegantonyan/pundit,yakovenkodenis/pundit,rickypchen/pundit,stefania11/pundit,xuwupeng2000/pundit,selaromi/pundit,thewatts/pundit,goodylabs/pundit,justin808/pundit,ikhakoo/pundit