Fix a tiny little typo in documentation

No much to say here.

Author: bobey

docs/quick_tour.md

@@ -57,7 +57,7 @@ $consumer->acknowledge($message);
 
 ## Consumption 
 
-Consumption is a layer build on top of a transport functionality. 
+Consumption is a layer built on top of a transport functionality. 
 The goal of the component is to simply consume messages. 
 The `QueueConsumer` is main piece of the component it allows binding of message processors (or callbacks) to queues. 
 The `consume` method starts the consumption process which last as long as it is not interrupted.