bump atc
bump atc

[finishes #103162048]

Submodule src/github.com/concourse/atc 3137dc4..2796699:
  > clearer error for missing worker
  > when containers disappear from workers, reap in db

zachgersh/concourse,cjcjameson/concourse,zachgersh/concourse,zachgersh/concourse,concourse/concourse,longnguyen11288/concourse,concourse/concourse,concourse/concourse,CloudCredo/concourse,CloudCredo/concourse,concourse/concourse,cjcjameson/concourse,cjcjameson/concourse,longnguyen11288/concourse,CloudCredo/concourse,longnguyen11288/concourse,concourse/concourse