[#44] Upgrade Mathics, remove deadsnakes dependency

The deadsnakes PPA has apparently not been updated for compatibility
with Ubuntu Groovy, so the build was failing. I think we only needed
deadsnakes (which provides older Python versions) for Mathics,
which (until the recent new release) had a bug that prevented using it
with Python 3.8. By upgrading Mathics, we remove the need for the old
Python version, which means we don't have to figure out how to work
around the deadsnakes compatibility problem.

scripts/docker-install-phase1.bash

@@ -40,7 +40,5 @@ deb https://dl.yarnpkg.com/debian/ stable main
 deb https://downloads.ceylon-lang.org/apt/ unstable main
 EOF
 
-add-apt-repository -y -n ppa:deadsnakes/ppa
-
 popd >/dev/null
 rm "$0"

scripts/docker-install-phase3c.bash

@@ -17,10 +17,6 @@ m4
 # MariaDB
 libtinfo5
 
-# Mathics
-python3.7
-python3.7-dev
-
 # MiniZinc
 minizinc
 

scripts/docker-install-phase3d.bash

@@ -84,7 +84,8 @@ vim
 mono-vbnc
 
 # Wolfram Language
-python3.7
+python3
+python3-dev
 
 # x86
 clang

scripts/docker-install-phase5.bash

@@ -126,7 +126,7 @@ npm install -g vim-language-server
 pip3 install whitespace
 
 # Wolfram Language
-python3.7 -m pip install mathics
+pip3 install Mathics3
 
 rm -rf /root/.cache /root/.config /root/.cpan /root/.cpanm /root/.dub /root/.gem /root/.npm /root/.npmrc
 rm -f /tmp/core-js-banners