Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Eric Malm:
     Add configuration option to enable writing billing events ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/19543527 )
     Reorganize Rubocop TODO file. ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/19533440 )
     Remove all assignments in conditionals. ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/19532664 )
     Fix AmbiguousOperator Rubocop warnings. ( Travis Unknown )
     Remove extraneous presenter spec fixtures. ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/19522104 )
     Switch alias to alias_method ( Travis Failed: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/19521293 )
     Ignore vendor directory during Rubocop run ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/19518313 )
  Abhijit Hiremagalur:
     Introduce Rubocop ( Travis Unknown )
     Fix Rubocop violations ( Travis Unknown )