Update url in install instructions

Doc has changed, old link gets redirected to the new one. Adapting link here to point to the new target.

eZ/Bundle/EzPublishCoreBundle/Composer/ScriptHandler.php

@@ -130,7 +130,7 @@ public static function installWelcomeText(Event $event)
 
 
 For full install instructions, including setting up full web server & directory permissions, see:
-https://doc.ezplatform.com/en/latest/getting_started/install_using_composer/
+https://doc.ezplatform.com/en/latest/getting_started/install_ez_platform/
 
 EOT
         );