Update StockExchange example from mediator pattern

src/MediatorPattern/MediatorPatternExamples.cs

@@ -27,6 +27,8 @@ namespace MediatorPattern
             FlightAirTrafficControlExample flightAirControl = new FlightAirTrafficControlExample();
             flightAirControl.Run();
 
+            GoToNextStep();
+
             //Taxi/Taxi center example
             //Chat application
             //GUI libraries

src/MediatorPattern/StockExchange/StockExchange.cs

@@ -69,7 +69,7 @@ namespace MediatorPattern.StockExchange
             if (!couldSellStocks)
             {
                 AddSeller(trader);
-                Console.WriteLine("No seller buys it at this price, try a lower price");
+                Console.WriteLine("No buyer buys it at this price, try a lower price");
             }