fix(endWith): wrap args - they are not observables - in of before concatenating

spec/operators/endWith-spec.ts

@@ -20,6 +20,16 @@ describe('endWith operator', () => {
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
 
+  it('should append numbers to a cold Observable', () => {
+    const values = { a: 1, b: 2, c: 3, s: 4 };
+    const e1 =  cold('---a--b--c--|', values);
+    const e1subs =   '^           !';
+    const expected = '---a--b--c--(s|)';
+
+    expectObservable(e1.pipe(endWith(values.s))).toBe(expected, values);
+    expectSubscriptions(e1.subscriptions).toBe(e1subs);
+  });
+
   it('should end an observable with given value', () => {
     const e1 =   hot('--a--|');
     const e1subs =   '^    !';

src/internal/operators/endWith.ts

@@ -1,5 +1,6 @@
 import { Observable } from '../Observable';
 import { concat } from '../observable/concat';
+import { of } from '../observable/of';
 import { MonoTypeOperatorFunction, SchedulerLike, OperatorFunction } from '../types';
 
 /* tslint:disable:max-line-length */
@@ -62,5 +63,5 @@ export function endWith<T, Z = T>(...array: Array<Z | SchedulerLike>): OperatorF
  * @owner Observable
  */
 export function endWith<T>(...array: Array<T | SchedulerLike>): MonoTypeOperatorFunction<T> {
-  return (source: Observable<T>) => concat(source, ...(array as any[])) as Observable<T>;
+  return (source: Observable<T>) => concat(source, of(...array)) as Observable<T>;
 }