change docker to use python3.9

Dockerfile

@@ -21,7 +21,7 @@
 #     --server.enableXsrfProtection false \
 #     --server.fileWatcherType none
 
-FROM python:3.9-slim
+FROM python:3.9
 WORKDIR /app
 COPY requirements.txt ./requirements.txt
 RUN pip install -r requirements.txt