Bump installation to v3.

Author: yajra

README.md

@@ -23,7 +23,7 @@ This version is still on experimental stage. Until Laravel DataTables v8.x stabl
 there might be a breaking changes that may be included on future releases. 
 
 ## Quick Installation
-`composer require yajra/laravel-datatables-buttons:^2.0`
+`composer require yajra/laravel-datatables-buttons:^3.0`
 
 #### Service Provider (Optional on Laravel 5.5)
 `Yajra\DataTables\ButtonsServiceProvider::class`