Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Graeme Davison and James Myers:
     Updating an AppSecurityGroup to a running or staging default is now a PUT ( Travis created: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28361947 )
  Zach Robinson:
     Remove serialization model shared examples ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28361722 )
     Remove stripped_string_attributes from shared model examples ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28335792 )
     Remove call to missing shared examples ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28334826 )
     Remove unique_attributes from shared model examples ( Travis finished: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28334273 )
  Michael Fraenkel:
     Bump vendor/errors to latest ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28321348 )
     Sort the buildpacks by priority via the Controller ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28318209 )
  Julian Friedman:
     defensive check for 0 shas in resource_match ( Travis Unknown )
  Onsi Fakhouri:
     enhance droplet download to redirect to non-local ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28273086 )
  Joseph Palermo:
     Remove required_attributes from shared model examples ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/28272945 )