Travis CI: Add Python 3.7 to the testing (#881)

* Travis CI: Add Python 3.7 to the testing

In alignment with travis-ci/travis-ci#9069

* Travis CI: py37-flake8

* tox.ini: testenv:py37-flake8

* Upgrade tox requirement to >= 3.1.3

Enables Py38, Py39, Py40, etc.

* Force a retest

* Remove trailing whitespace

* tox.ini: Add py38 for Python 3.8.0a0

* Update minversion in tox.ini to match dev-requirements.txt

.travis.yml

@@ -23,14 +23,22 @@ matrix:
       env: TOXENV=py35
     - python: 3.6
       env: TOXENV=py36
-    - python: nightly
+    - python: 3.7
       env: TOXENV=py37
+      dist: xenial    # required for Python 3.7 (travis-ci/travis-ci#9069)
+      sudo: required  # required for Python 3.7 (travis-ci/travis-ci#9069)
+    - python: nightly
+      env: TOXENV=py38
+      dist: xenial    # required for Python 3.8 (travis-ci/travis-ci#9069)
+      sudo: required  # required for Python 3.8 (travis-ci/travis-ci#9069)
     - python: pypy
       env: TOXENV=pypy
     - python: 2.7
       env: TOXENV=py27-flake8
-    - python: 3.6
-      env: TOXENV=py36-flake8
+    - python: 3.7
+      dist: xenial    # required for Python 3.7 (travis-ci/travis-ci#9069)
+      sudo: required  # required for Python 3.7 (travis-ci/travis-ci#9069)
+      env: TOXENV=py37-flake8
     - env: TOXENV=docstrings
     - env: TOXENV=notebooks
     - env: TOXENV=readme

dev-requirements.txt

@@ -5,4 +5,4 @@ pytest>=2.3.5,<3.3.0
 wheel==0.21.0
 betamax>=0.5.0
 betamax_matchers>=0.2.0
-tox>=2.5.0
+tox>=3.1.3

tox.ini

@@ -1,6 +1,6 @@
 [tox]
-envlist = py{27,34,35,36,py},py{27,36}-flake8,doclint,commitlint,docstrings
-minversion = 2.5.0
+envlist = py{27,34,35,36,37,38,py},py{27,37}-flake8,doclint,commitlint,docstrings
+minversion = 3.1.3
 
 [testenv]
 passenv = GH_* APPVEYOR*
@@ -20,7 +20,7 @@ deps =
     flake8
 commands = flake8 {posargs} src/github3/ tests/unit/ tests/integration/
 
-[testenv:py36-flake8]
+[testenv:py37-flake8]
 deps =
     {[testenv:py27-flake8]deps}
 commands = flake8 {posargs} src/github3/ tests/unit/ tests/integration/