bump atc
bump atc

[finishes #110861806]

Submodule src/github.com/concourse/atc b0a7224..24b33e3:
  > debian wheezy needs older version of gcc/g++

Signed-off-by: Corbin Halliwill <38cf05332854d0c00b392ad9da3fb5cec295aa83@pivotal.io>

zachgersh/concourse,concourse/concourse,cjcjameson/concourse,concourse/concourse,concourse/concourse,zachgersh/concourse,cjcjameson/concourse,concourse/concourse,zachgersh/concourse,cjcjameson/concourse,concourse/concourse