added module declaration ("declare module")

[andreash]

The d.ts file is missing a module declaration for typescript to work. Without the declaration, typescript does not accept, for example Validator as a constructable expression.

[icebob]

Could you show an example when it causes issue?

[erfanium]

and I guess this will break the module in other runtime like deno. because they don't have such a module concept like what node does.