docs(README): Fix 2.x doc link

Author: mportuga

README.md

@@ -166,7 +166,7 @@ The full list of SauceLabs browsers can be seen by running `grunt saucebrowsers`
 
 As of the 3.0 release, 2.x is officially deprecated. There will be no further releases. If for some reason you need to find the 2.x source please see the [2.x branch](https://github.com/angular-ui/ng-grid-legacy).
 
-The 2.x docs are here: [http://angular-ui.github.io/ui-grid/](http://angular-ui.github.io/ui-grid/).
+The 2.x docs are here: [https://github.com/angular-ui/ng-grid-legacy/wiki](https://github.com/angular-ui/ng-grid-legacy/wiki).
 
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