travis: update to focal

This updates to Ubuntu 20.04 (focal) and uses it's provided Meson version.

Signed-off-by: Stephan Lachnit <stephanlachnit@protonmail.com>

.travis.yml

@@ -1,4 +1,4 @@
-dist: xenial
+dist: focal
 language: c
 compiler: gcc
 sudo: false
@@ -7,20 +7,13 @@ addons:
     packages:
       - clang
       - clang-format
-      - python3-pip
-      - python3-setuptools
       - libsystemd-dev
-      - ninja-build
       - libdbus-1-dev
+      - meson
   artifacts:
     paths:
     - $(git ls-files -o | tr "\n" ":")
 
-before_script:
-  - pip3 install wheel
-  - pip3 install --upgrade 'meson==0.52.0'
-  - meson --version
-
 script:
   - ./scripts/format-check.sh
   - ./bootstrap.sh -Dwith-examples=true