bump atc
bump atc

[finishes #97654516]

Submodule src/github.com/concourse/atc 6dc9a76..6d9fce6:
  > do not lie chris you are a badman
  > save status of a step that has already finished
  > remove empty test example
  > do not try to resume a build that has finished

squeedee/concourse,cjcjameson/concourse,zachgersh/concourse,CloudCredo/concourse,longnguyen11288/concourse,squeedee/concourse,CloudCredo/concourse,squeedee/concourse,beni55/concourse,cjcjameson/concourse,holgero/concourse,sedouard/concourse,concourse/concourse,holgero/concourse,longnguyen11288/concourse,sedouard/concourse,CloudCredo/concourse,holgero/concourse,Amit-PivotalLabs/concourse,concourse/concourse,concourse/concourse,concourse/concourse,Amit-PivotalLabs/concourse,longnguyen11288/concourse,sedouard/concourse,zachgersh/concourse,cjcjameson/concourse,concourse/concourse,zachgersh/concourse,beni55/concourse,Amit-PivotalLabs/concourse,beni55/concourse