add Lazy Type

[Ryomasao]

Hi! I want to use Yup.lazy, but I get a type error.

https://codesandbox.io/s/lingering-frog-0bryw?file=/src/App.tsx

It worked fine when I changed the type to any, so I added the Lazy type to Schema.
Lazy seems to be the same as the Schema type.

// tslint:disable-next-line:no-empty-interface
export interface Lazy extends Schema<any> {}

[bluebill1049]

Thanks @Ryomasao