Upgrade to Python3

Dockerfile

-FROM ubuntu:18.04
- 
+FROM python:3.9-buster
+
 LABEL maintainer="Suhas CV sc4817@rit.edu"
  
 RUN apt-get update -y && \
-    apt-get install -y python-pip python-dev latexml libtext-unidecode-perl zip
+    apt-get install -y latexml libtext-unidecode-perl zip
 
 COPY . /app
 COPY templates /app/templates