build(docker): WORKDIR /var/lib/duniter

In line with Duniter home.

release/docker/Dockerfile

@@ -61,7 +61,7 @@ EXPOSE 9220 10901 20901 30901
 
 # use duniter user
 USER duniter
-WORKDIR /duniter
+WORKDIR /var/lib/duniter
 
 ENTRYPOINT ["/docker-entrypoint.sh"]
 CMD []