bump atc
bump atc

concourse/concourse#1705

Submodule src/github.com/concourse/atc cc50e92d..e887de62:
  > Dashboard: block click event to pipeline behind footer

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

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