message: chore: remove explicit types in toPromise spec
  As toPromise can resolve to undefined via the change in
diff: @@ -4,7 +4,7 @@ import { of, EMPTY, throwError, config } from 'rxjs';
  /** @test {toPromise} */
  describe('Observable.toPromise', () => {
  it('should convert an Observable to a promise of its last value', (done: MochaDone) => {
  - of(1, 2, 3).toPromise(Promise).then((x: number) => {
  + of(1, 2, 3).toPromise(Promise).then(x => {
  expect(x).to.equal(3);
  done();
  });
  @@ -33,7 +33,7 @@ describe('Observable.toPromise', () => {
  return new Promise(callback as any);
  } as any;
  - of(42).toPromise().then((x: number) => {
  + of(42).toPromise().then(x => {
  expect(wasCalled).to.be.true;
  expect(x).to.equal(42);
  done();
  