Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Nicholas Calugar and Zach Robinson:
     implement purge and reseed functionality for service usage events. ( Travis created: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/25259154 )
  Alex Suraci:
     fix up diego spec ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/25258668 )
     send detected start command ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/25205295 )
     save app's detected start command on staging completion ( Travis Unknown )