tests: switch to Ubuntu Bionic, use pylint3 to lint Python scripts (Travis CI)

.travis.yml

@@ -1,4 +1,4 @@
-dist: xenial
+dist: bionic
 sudo: required
 language: c
 
@@ -20,13 +20,11 @@ matrix:
         env: BUILDTOOL="cmake" BUILDARGS="-DENABLE_CODE_COVERAGE=ON" CODECOVERAGE="1"
 
 before_script:
-    - rm -rf "$HOME/.pyenv"
-    - sudo rm -rf /opt/pyenv
     - echo 'APT::Install-Recommends "false";' | sudo tee -a /etc/apt/apt.conf
     - travis_retry sudo apt-get update -qq
-    - travis_retry sudo apt-get -y install devscripts equivs python-pip libenchant-dev autopoint cmake lcov pkg-config libncursesw5-dev gem2deb libperl-dev python-dev python3-dev libaspell-dev liblua5.3-dev tcl8.6-dev guile-2.0-dev libv8-dev libcurl4-gnutls-dev libgcrypt20-dev libgnutls-dev zlib1g-dev curl libcpputest-dev php7.0-dev libphp7.0-embed
+    - travis_retry sudo apt-get -y install devscripts equivs python-pip libenchant-dev autopoint cmake lcov pkg-config libncursesw5-dev gem2deb libperl-dev python-dev python3-dev libaspell-dev liblua5.3-dev tcl8.6-dev guile-2.0-dev libv8-dev libcurl4-gnutls-dev libgcrypt20-dev libgnutls28-dev zlib1g-dev curl libcpputest-dev php7.2-dev libphp7.2-embed libargon2-0-dev libsodium-dev pylint3
     - travis_retry sudo gem install asciidoctor
-    - travis_retry sudo -H pip install --ignore-installed msgcheck pylint
+    - travis_retry sudo -H pip install --ignore-installed msgcheck
     - phpenv local system
       # work around broken travis environment variables, see https://github.com/travis-ci/travis-ci/issues/5301
     - unset PYTHON_CFLAGS
@@ -34,10 +32,11 @@ before_script:
 script:
     - ./tools/build-test.sh
     - msgcheck po/*.po
-    - pylint --version
-    - pylint tests/scripts/python/testapigen.py
-    - pylint tests/scripts/python/testapi.py
-    - pylint tests/scripts/python/unparse.py
+    - pylint3 --version
+    - pylint3 --additional-builtins=_ doc/docgen.py
+    - pylint3 tests/scripts/python/testapigen.py
+    - pylint3 tests/scripts/python/testapi.py
+    - pylint3 tests/scripts/python/unparse.py
     - ./tools/build-debian.sh test-patches
 
 after_success:

ChangeLog.adoc

@@ -54,6 +54,7 @@ Documentation::
 
 Tests::
 
+  * core: switch to Ubuntu Bionic on Travis CI, use pylint3 to lint Python scripts
   * irc: add tests on IRC color functions
 
 Build::