Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  David Sabeti and Matt Royal:
     Fix bug in migration ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/20324588 )
  Eric Malm:
     Remove a redudant test, which might cause flakiness. ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/20323460 )
  Ruth Byers:
     API spec for filtering private domains by name ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/20320584 )
     API spec for querying shared domains by name ( Travis Unknown )
  Onsi Fakhouri:
     don't explode if the stager_response has no streaming_log_url ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/20317358 )
  Tammer Saleh:
     Merge branch 'brahmaroutu-rest_api_documentation' ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/20308393 )
     Api specs should not reach under the hood ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/20308031 )
  Karl Isenberg:
     Update app bits api spec to better describe multipart application uploading. ( Travis Unknown )
  Srini Brahmaroutu:
     adding REST API documentation for uploading and downloading app ( Travis Unknown )