bump atc
bump atc

concourse/concourse#1554

Submodule src/github.com/concourse/atc 9f4d4f6e..cd954b96:
  > Dashboard: anchor links on team groups

Signed-off-by: Gabriel Dumitrescu <ac98dc248ba95b80e235d49d71a9a50afc4ea93d@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse