Update README.md

Author: emteknetnz

README.md

@@ -27,7 +27,7 @@ This branch will aim for compatibility with SilverStripe 4.x.
 
 ## Installation
 ```bash
-composer require symbiote/silverstripe-gridfieldextensions "^3"
+composer require symbiote/silverstripe-gridfieldextensions:^3
 ```
 
 For SilverStripe 3.x, please see the [compatible branch](https://github.com/symbiote/silverstripe-gridfieldextensions/tree/2).