Update readme with confirmation that 5.1 Laravel works

Author: pionl

README.md

@@ -23,7 +23,7 @@ and updates the other entries based on the models position value.
 
 ## Installation
 
-> Tested in Laravel 5.3 - 5.6, should work in all 5.* releases
+> Tested in Laravel 5.1 - 5.6, should work in all 5.* releases
 
 **Install via composer**