Fix version.

Author: yajra

readme.md

@@ -3,5 +3,5 @@
 ## Contribution Guidelines
 
 If you are submitting documentation for the **current stable release**, submit it to the corresponding branch.
-For example, documentation for Laravel Datatables 5.1 would be submitted to the `5.1` branch.
+For example, documentation for Laravel Datatables 6.0 would be submitted to the `6.0` branch.
 Documentation intended for the next release of Laravel Datatables should be submitted to the `master` branch.