Corrected successSubscriber to documentSubscriber for two await calls in reactive QuickTour (#962)

Author: wbleonard

driver-reactive-streams/src/examples/reactivestreams/tour/QuickTour.java

@@ -127,12 +127,12 @@ public static void main(final String[] args) {
         // now use a range query to get a larger subset
         documentSubscriber = new PrintDocumentSubscriber();
         collection.find(gt("i", 50)).subscribe(documentSubscriber);
-        successSubscriber.await();
+        documentSubscriber.await();
 
         // range query with multiple constraints
         documentSubscriber = new PrintDocumentSubscriber();
         collection.find(and(gt("i", 50), lte("i", 100))).subscribe(documentSubscriber);
-        successSubscriber.await();
+        documentSubscriber.await();
 
         // Sorting
         documentSubscriber = new PrintDocumentSubscriber();