docs: Fix demo container name

Author: hangy

extras/docker/demo/README.md

@@ -25,11 +25,11 @@ Then just open <http://localhost:8000> and log in as: **admin**, password **admi
 
 To stop the container:
 
-```sudo docker container stop wger.apache```
+```sudo docker container stop wger.demo```
 
 To start developing again:
 
-```sudo docker container start --attach wger.apache```
+```sudo docker container start --attach wger.demo```
 
 
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