Update README.md

Author: GrahamCampbell

README.md

@@ -5,7 +5,7 @@ A lock manager for Laravel 5.
 
 ## Installation
 
-This version requires [PHP](https://php.net) 7.1 or 7.2, and supports Laravel 5.5 - 5.7 only.
+This version requires [PHP](https://php.net) 7.1 - 7.3, and supports Laravel 5.5 - 5.8 only.
 
 To get the latest version, simply require the project using [Composer](https://getcomposer.org):