bump atc
bump atc

[finishes #100234914]

Submodule src/github.com/concourse/atc cd5a207..6f0ddd8:
  > improve err checking around registerJob

longnguyen11288/concourse,longnguyen11288/concourse,beni55/concourse,zachgersh/concourse,concourse/concourse,holgero/concourse,CloudCredo/concourse,concourse/concourse,sedouard/concourse,CloudCredo/concourse,CloudCredo/concourse,beni55/concourse,beni55/concourse,longnguyen11288/concourse,concourse/concourse,zachgersh/concourse,cjcjameson/concourse,zachgersh/concourse,holgero/concourse,concourse/concourse,sedouard/concourse,sedouard/concourse,concourse/concourse,cjcjameson/concourse,holgero/concourse,cjcjameson/concourse