bump atc
bump atc

[finishes #127510245]

Submodule src/github.com/concourse/atc 78adb1c..f82cc3f:
  > buildreaper gets active jobs instead of dashboard

concourse/concourse,cjcjameson/concourse,concourse/concourse,cjcjameson/concourse,cjcjameson/concourse,concourse/concourse,concourse/concourse,concourse/concourse