fix(groupBy): unsubscribe GroupDurationSubscriber after completing th…

…e group

The Groups are disposed by the GroupDurationSelector, however the
GroupDurationSubscriber can be subscribed to a different observable
than the group itself. To prevent any unwanted subscriptions to
accumulate over time we need to explicitly unsubscribe after the
first event in GroupDurationSubscriber closes the group.

Fixes #2660

src/operator/groupBy.ts

@@ -240,6 +240,7 @@ class GroupDurationSubscriber<K, T> extends Subscriber<T> {
       group.error(err);
     }
     this.parent.removeGroup(this.key);
+    this.unsubscribe();
   }
 
   protected _complete(): void {
@@ -248,6 +249,7 @@ class GroupDurationSubscriber<K, T> extends Subscriber<T> {
       group.complete();
     }
     this.parent.removeGroup(this.key);
+    this.unsubscribe();
   }
 }