message: test(last): remove invalid call
diff: @@ -163,8 +163,6 @@ describe('Observable.prototype.last', () => {
  // After the type guard `last` predicates, the type is narrowed to string
  xs.pipe(last(isString))
  .subscribe(s => s.length); // s is string
  - xs.pipe(last(isString, s => s.substr(0))) // s is string in predicate)
  - .subscribe(s => s.length); // s is string
  // boolean predicates preserve the type
  xs.pipe(last(x => typeof x === 'string'))
  