Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Phan Le:
     Change app_usage_events reset endpoint to return 204 ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/15798983 )
     Using truncate is non-transactional so the test can't be. ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/15798454 )
     Remove desired instances and desired memory from audit events. ( Travis Unknown )
     Move field section to the right request ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/15796935 )
     Delete flakey tests. Why should we test private methods anyway? ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/15796549 )