Fix Docker entrypoint typo

docker/entrypoint.sh

@@ -1,10 +1,10 @@
 #!/bin/sh
 
 export USER=opengist
-PID=${PID:-1000}
+UID=${UID:-1000}
 GID=${GID:-1000}
 groupmod -o -g "$GID" $USER
-usermod -o -u "$PID" $USER
+usermod -o -u "$UID" $USER
 
 chown -R "$USER:$USER" /opengist