docker: Update to the use of Python 3.9

Getting with the times

#4 - Investigate extending pr0xy to use SAM

contained/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine
+FROM python:3.9-alpine
 
 RUN apk add --no-cache \
 	bash \
@@ -8,7 +8,6 @@ RUN apk add --no-cache \
 	iptables \
 	git \
 	netcat-openbsd \
-	python3 \
 	ulogd \
 	tcpdump \
 	wget