use new ubuntu 20.04 as base image

Dockerfile

@@ -1,9 +1,7 @@
-FROM python:3.8-slim-buster
+FROM ubuntu:20.04
 
-RUN apt-get update && apt-get install --no-install-recommends -y libcap2-bin && rm -rf /var/lib/apt/lists/*
-RUN setcap cap_net_bind_service=+ep /usr/local/bin/python3.8
-
-RUN pip3 --no-cache-dir install cryptography uvloop
+RUN apt-get update && apt-get install --no-install-recommends -y python3 python3-uvloop python3-cryptography libcap2-bin && rm -rf /var/lib/apt/lists/*
+RUN setcap cap_net_bind_service=+ep /usr/bin/python3.8
 
 RUN useradd tgproxy -u 10000