Merge branch 'backport_pr_340' into '3.7-maintenance'

[3.7] Fix travis-ci

See merge request pycqa/flake8!368

.travis.yml

@@ -1,11 +1,11 @@
-sudo: false
+dist: xenial
 language: python
 cache: pip
 before_script:
-- pip install tox
+- pip install --upgrade tox setuptools virtualenv
 
 # test script
-script:  tox
+script: tox
 notifications:
   on_success: change
   on_failure: always
@@ -20,20 +20,19 @@ matrix:
       env: TOXENV=py35
     - python: 3.6
       env: TOXENV=py36
-    # https://github.com/travis-ci/travis-ci/issues/9069
-    #- python: 3.7
-    #  env: TOXENV=py37
+    - python: 3.7
+      env: TOXENV=py37
     - python: pypy
       env: TOXENV=pypy
     - python: 2.7
       env: TOXENV=readme
-    - python: 3.4
+    - python: 3.7
       env: TOXENV=flake8
-    - python: 3.4
+    - python: 3.7
       env: TOXENV=pylint
-    - python: 3.4
+    - python: 3.7
       env: TOXENV=doc8
-    - python: 3.4
+    - python: 3.7
       env: TOXENV=bandit
-    - python: 3.4
+    - python: 3.7
       env: TOXENV=docs