Upgrade Dockerfile to use Python3 docker hub image

Python 2.x is deprecated, and so things should be Python 3 long term.

Author: mtompset

Dockerfile

@@ -1,10 +1,10 @@
-FROM alpine:3.11
+FROM python:3-alpine
 
 RUN apk update \
  && apk add --no-cache \
             bash \
             mysql-client \
-            python py-pip \
+ && python -m pip install --upgrade pip \
  && pip install s3cmd python-magic
 
 COPY application/ /data/