upgrade base image

Dockerfile

 
-FROM debian:stretch 
+FROM debian:bullseye 
     
 # Python Packages 
-RUN apt-get update && apt-get install -y \ 	
-    python3 \ 	
+RUN apt-get update && apt-get install -y \
+    python3 \
     python3-pip 
 
-# Upgrade pip    
-RUN pip3 install --upgrade pip 
-
 # pip Packages
 RUN pip3 install \     
     flask==1.0.2 \