bump atc
bump atc

Submodule src/github.com/concourse/atc 641f439..97cda28:
  > Merge branch 'dolph-anchors-be-clickable'

closes concourse/atc#166

Signed-off-by: Maria Shaldibina <dc03896a0185453e5852a5e0f0fab6cbd2e026ff@pivotal.io>

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