Update compose to version 3.3

Thanks @renich!

docker-compose.yml

@@ -3,16 +3,19 @@
 # pypiserver docker-compose example
 ########################################################################
 
-version: "3"
+version: "3.3"
 
 services:
     pypiserver:
-    image: pypiserver:latest
+        image: pypiserver/pypiserver:latest
         volumes:
-      # Mount local /tmp/pypiserver to /data in container
-      - /tmp/pypiserver:/data
+            - type: bind
+              source: ./data
+              target: /data
         # Use an .htaccess file to control access, serve packages from
-    # /tmp/pypiserver/packages (/data/packages in the container)
+        # ./data (which will be /data in the container)
         command: -P /data/.htaccess -a update,download,list /data/packages
         ports:
             - "80:8080"
+volumes:
+    data: