- modernize Travis config

.travis.yml

@@ -1,28 +1,32 @@
 language: python
-sudo: false
-python:
-    - 2.7
-    - 3.5
-    - 3.6
+
 matrix:
     include:
         - python: "3.7"
+          env: TOXENV=flake8
+        - python: "3.7"
+          env: TOXENV=coverage
+          after_success:
+              - coveralls
+        - python: "2.7"
+          env: TOXENV=py27
+        - python: "3.5"
+          env: TOXENV=py35
+        - python: "3.6"
+          env: TOXENV=py36
+        - python: "3.7"
+          env: TOXENV=py37
           dist: xenial
         - python: "3.8-dev"
+          env: TOXENV=py38
           dist: xenial
 
 install:
-    - pip install -U setuptools
-    - pip install coveralls coverage
-    - pip install zc.buildout
-    - buildout bootstrap
-    - buildout
+    - travis_retry pip install -U pip setuptools tox
+    - travis_retry pip install -U coverage coveralls
 
 script:
-    - coverage run bin/test -v1
-after_success:
-    - coverage combine
-    - coveralls
+    - travis_retry tox
 
 notifications:
     email: false