Update README.md

Author: GrahamCampbell

README.md

@@ -9,7 +9,7 @@
 
 ## Installation
 
-This version requires [PHP](https://php.net) 7, and supports [PHPUnit](https://phpunit.de/) 6 - 8 and Laravel 5.1+.
+This version requires [PHP](https://php.net) 7.0-7.4, and supports [PHPUnit](https://phpunit.de/) 6-8 and Laravel 5.1-5.8 and 6.
 
 To get the latest version, simply require the project using [Composer](https://getcomposer.org):