bump atc
bump atc

concourse/concourse#1835

Submodule src/github.com/concourse/atc 3f557699..c6e49a4c:
  > Dashboard: update animation for running pipeline states

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

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