sucker_punch now requires initializer for Rails <5.0

[Bob Walsh]

https://github.com/brandonhilkert/sucker_punch#active-job

If you want to use Sucker Punch version 2.0.0+ with Rails < 5.0.0, be sure to include the backwards compatibility module in an initializer:

( in config/initializers/sucker_punch.rb)

require 'sucker_punch/async_syntax'