Update type validation specs

Two tests using ensure_validation_of were still passing even though they
didn't have 'unresolved' in the array which should match the supported
types of mappings. Since they continue to pass as long as all elements
of the array the matcher receives are valid (even if the array is empty),
I think the clearest thing to do here is to just pass it Mapping::SUPPORTED_TYPES.
Merge pull request #326 from alphagov/update_validate_inclusion_specs

Update type validation specs