Update STM32 build to use Ubuntu 20.04

No need for a PPA, also gives it a newer GCC than the Linux build...

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 5c7c9f0..40cbd2c 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -53,25 +53,24 @@
         edge: true

 

     - name: "STM32"

+      dist: focal

       env:

         - TOOLCHAIN=../32blit.toolchain

         - RELEASE_FILE=${TRAVIS_BUILD_DIR}${REPO}-${TRAVIS_TAG}-${TRAVIS_BUILD_NUMBER}-STM32

       addons:

         apt:

-          sources:

-            sourceline: "ppa:daft-freak/arm-gcc"

-          packages:

-            gcc-arm-none-eabi

-            libnewlib-arm-none-eabi

-            libstdc++-arm-none-eabi-newlib

-            python3-pip

-            python3-setuptools

-            zip

+          gcc-arm-none-eabi

+          libnewlib-arm-none-eabi

+          libstdc++-arm-none-eabi-newlib

+          python2

+          python3-pip

+          python3-setuptools

+          zip

       install:

         - python3 -m pip install 32blit bitstring construct

       after_success:

         - curl -O https://raw.githubusercontent.com/danvk/travis-weigh-in/adcc3a3e5bc16b360aa379d0fc23c3a6e1d9b21d/weigh_in.py

-        - python weigh_in.py firmware/flash-loader/flash-loader.bin

+        - python2 weigh_in.py firmware/flash-loader/flash-loader.bin

       before_deploy:

         - make install

         - tar -zcf ${RELEASE_FILE}.tar.gz bin/