Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Phan Le:
     Endpoint to clear AppUsageEvent data and seed it with currently running apps ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/15793639 )
  Eric Malm:
     Split up Rakefile into smaller files ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/15792664 )
     Prefer new allow syntax for consistency ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/15791506 )
     Add clockwork to schedule tasks ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/15791402 )