Type definitions for Options.resolve() are not allowing custom resolvers

Type definition for Interface Options.resolver https://github.com/APIDevTools/swagger-parser/blob/main/lib/index.d.ts#L235-L243 is not allowing custom resolver.

Correct type definition inside [json-schema-ref-parser](https://github.com/APIDevTools/json-schema-ref-parser/blob/main/lib/index.d.ts#L202-L212)