Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Simon Leung:
     Remove duplicate validation in DockerPolicy ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/35046723 )
     Remove duplicate validation from Backends ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/35043349 )
  Max Brunsfeld:
     Make App#buildpack_specified? do what it says, not the opposite ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/34942985 )

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotallabs.com>