Switched to US spelling of `cancelled` in schema validation
Switched to US spelling of `cancelled` in schema validation

refs https://github.com/TryGhost/Team/issues/2030

- we tend to use US spellings in the code and this was merged with the
  British spelling
- nothing has been added to this table yet so it's safe to switch

TryGhost/Ghost,TryGhost/Ghost,TryGhost/Ghost