Dockerfile: Fix permission on data volumes

docker/Dockerfile

@@ -1,20 +1,21 @@
 FROM alpine
 MAINTAINER Polyconseil <opensource+dokang@polyconseil.fr>
 
-ENV PYTHONPATH=/home/dokang
-VOLUME ['/home/dokang/data']
 EXPOSE 6543
 
+RUN apk add --no-cache --update python3
 RUN adduser -u 998 -D dokang
+
 COPY ./files /home/dokang/
+RUN mkdir /home/dokang/data
 RUN chown -R dokang:dokang /home/dokang
-
-RUN apk add --no-cache --update python3
+VOLUME ['/home/dokang/data']
 
 USER dokang
 WORKDIR /home/dokang
 
 RUN python3 -m venv venv && \
     venv/bin/pip install dokang dokang_pdf waitress
 
+ENV PYTHONPATH=/home/dokang
 ENTRYPOINT ["/home/dokang/venv/bin/python3", "entrypoint.py"]