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