Update README.md

Author: clarkeash

README.md

@@ -20,7 +20,7 @@ Validates a user submitted subdomain in your application.
   </a>
 </p>
 
-Supports Laravel: 5.5, 5.6 & 5.7
+Supports Laravel: 5.5, 5.6, 5.7 & 5.8
 
 ## Installation