Update docker image to Ubuntu 20.04

scripts/Dockerfile

@@ -4,7 +4,7 @@
 #	docker push termux/package-builder
 # This is done after changing this file or any of the
 # scripts/setup-{ubuntu,android-sdk}.sh setup scripts.
-FROM ubuntu:19.10
+FROM ubuntu:20.04
 
 # Fix locale to avoid warnings:
 ENV LANG en_US.UTF-8

scripts/get_hash_from_file.py

@@ -1,6 +1,6 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
-import os, sys
+import sys
 
 def get_pkg_hash_from_Packages(Packages_file, package, version, hash="SHA256"):
     with open(Packages_file, 'r') as Packages:

scripts/setup-ubuntu.sh

@@ -131,7 +131,7 @@ PACKAGES+=" gtk-3-examples"
 PACKAGES+=" gtk-doc-tools"
 PACKAGES+=" itstool"
 PACKAGES+=" libgdk-pixbuf2.0-dev"
-PACKAGES+=" python-xcbgen"
+PACKAGES+=" python3-xcbgen"
 PACKAGES+=" xfonts-utils"
 
 # Do not require sudo if already running as root.