Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Michael Fraenkel:
     Pick a different name to prevent name pollution ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/39046211 )
     Pass along the droplet and build artifact uris ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/39025946 )
  Matthew Sykes:
     Finish the rename s/CF_DIEGO/DIEGO/g ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/38962184 )
     update api version spec post-merge ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/38950274 )
     backfill test for `stage_with_diego?` ( Travis Unknown )
     remove 'required' option for diego configs [#80165358] ( Travis Unknown )
  Johannes Petzold:
     don't force staging on diego when running on diego ( Travis Unknown )
     rename DIEGO_BETA -> DIEGO_STAGE_BETA [#80165358] ( Travis Unknown )
  Rick Reilly and Serguei Filimonov:
     Deprecate /v2/app_events ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/38945989 )
  Chris Piraino and Eric Malm:
     Update copy bits API doc to make endpoint experimental ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/38855006 )