Update version from 4.0.0-beta2 to 4.0.0 (#161)

Author: skerbis

package.yml

@@ -1,5 +1,5 @@
 package: maintenance
-version: '4.0.0-beta2'
+version: '4.0.0'
 author: Friends Of REDAXO
 supportpage: https://github.com/FriendsOfREDAXO/maintenance
 title: translate:maintenance_title