fix(concat): handle a given scheduler correctly

Fix the static concat operator to handle the scheduler argument
correctly. Previously the scheduler argument was extracted
from the arguments array, then inserted back into the arguments
array, and the fromArray creation method did not receive the
scheduler as a Scheduler, but attempted to use it as an Observable, which
caused a scheduler-related test to fail.

src/operators/concat-static.ts

@@ -15,7 +15,6 @@ export default function concat<R>(...observables: Array<Observable<any> | Schedu
   let args = <any[]>observables;
   if (typeof (args[observables.length - 1]).schedule === 'function') {
     scheduler = args.pop();
-    args.push(1, scheduler);
   }
-  return (<CoreOperators<any>>Observable.fromArray(observables)).mergeAll(1);
+  return (<CoreOperators<any>>Observable.fromArray(observables, scheduler)).mergeAll(1);
 }