Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Max Brunsfeld:
     Return 503 from space summary when instance info is unavailable ( Travis created: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/31288595 )

Signed-off-by: Simon Leung <leungs@us.ibm.com>