Update offline-environment.md

Fix a relative address.
"generate_list.sh" file did not open correctly.

docs/operations/offline-environment.md

@@ -19,7 +19,7 @@ Then you need to setup the following services on your offline environment:
 * [Optional] an internal PyPi server for python packages used by Kubespray
 * [Optional] an internal Helm registry for Helm chart files
 
-You can get artifact lists with [generate_list.sh](/contrib/offline/generate_list.sh) script.
+You can get artifact lists with [generate_list.sh](https://github.com/kubernetes-sigs/kubespray/blob/master/contrib/offline/generate_list.sh) script.
 In addition, you can find some tools for offline deployment under [contrib/offline](/contrib/offline/README.md).
 
 ## Configure Inventory