change opsi link to fix 404

README.md

@@ -127,7 +127,7 @@
   * [Chocolatey](https://chocolatey.org/) – Windows CLI package manager written in .NET/PS, based on [NuGet](https://www.nuget.org/).
   * [just-install](http://just-install.it/) – Python script for downloading and silently installing MSI files.
   * [OCS Inventory NG](http://www.ocsinventory-ng.org/en/) - Inventory, deployment and network scan.
-  * [Opsi](http://www.opsi.org/en) (open PC server integration) - Client Management for Windows based on Debian.
+  * [Opsi](http://www.opsi.org) (open PC server integration) - Client Management for Windows based on Debian.
   * [WAPT](https://dev.tranquil.it/wiki/WAPT_-_apt-get_pour_Windows/en) - Network-wide (un)installation, configuration and upgrades of Windows based software.
   * [WPKG](http://wpkg.org/) - Software deployment, upgrade and removal program for Windows.