This commit fixes an issue where specifying a class like `Time`
for the `type` option in `expose` documentation resulted in an error
instead of generating the correct Swagger/OpenAPI specification.

This functionality was working correctly in v0.5.5 but regressed
after PR #75, leading to the following error:

```
GrapeSwagger::Errors::UnregisteredParser:
  No parser registered for Time.
```

The `primitive_type?` method now uses
`GrapeSwagger::DocMethods::DataType.call` to resolve the type
name before checking if it's a primitive type.
This ensures that types like `Time` are correctly identified as
strings with the `date-time` format, restoring the previous behavior.

Fix Correctly handle class types like Time in documentation