Implement a fix for the "ERROR Error: Observable cancelled prematurel…

…y" bug

apollographql#7608 (comment)

src/utilities/observables/Concast.ts

@@ -178,7 +178,7 @@ export class Concast<T> extends Observable<T> {
         // Delay unsubscribing from the underlying subscription slightly,
         // so that immediately subscribing another observer can keep the
         // subscription active.
-        if (sub) Promise.resolve().then(() => sub.unsubscribe());
+        if (sub) setTimeout(()=>{sub.unsubscribe()}, 0)
         this.sub = null;
         this.latest = ["error", error];
         this.reject(error);