Nested objects aren't typed as DeepMocked

[NickBolles]

export class MyClass {
  foo = {
    bar: () => {
      return 'foo.bar';
    },
  };
}

test('foo.bar', () => {
  const myMock = createMock<MyClass>();

  myMock.foo.bar.mockResolvedValue('foo.bar');
});

Based off the createMock source this nested object should also be a mock. Updating the typings as suggested in #884 fixes this error