Update README.md

Co-authored-by: John Nicholls <john@eagleeye.com>

README.md

@@ -11,7 +11,7 @@ Extensive changes were needed under the hood but the API should remain nearly
 identical with the exception of the exceptions thrown from the non-async client code.  
 
 Cases involving a non-existent entity (now including Add methods, such as trying to add a binding to a 
-non-existant vhost) are now uniformly thrown as RabbitMQ\Management\Exception\EntityNotFoundException
+non-existent vhost) are now uniformly thrown as RabbitMQ\Management\Exception\EntityNotFoundException
 where previously some were RabbitMQ\Management\Exception\RuntimeException.   Other exceptions from the 
 underlying Guzzle library are now passed through as GuzzleHttp\Exception\ClientException rather than
 GuzzleHttp\Exception\RequestException due to changes in Guzzle.