Improve testing

I believe that it would be nice to have tests
for actual and upcoming Python versions.

These changes also:

 - declare support for Python 3.7 at setup.py

 - remove Python 3.3 from tox's envlist

 - remove deprecated sudo option from .travis.yml

 - fix typos

.travis.yml

@@ -1,25 +1,60 @@
-sudo: false
 language: python
+dist: xenial
+
+stages:
+  - lint
+  - test
 
 matrix:
   include:
     - python: 2.7
       env: TOXENV=flake8
-    - python: 3.6
+      stage: lint
+
+    - python: 3.7
       env: TOXENV=py3flake8
+      stage: lint
+
     - python: 2.7
       env: TOXENV=py27
+      stage: test
+
     - python: 3.4
       env: TOXENV=py34
+      dist: trusty
+      stage: test
+
     - python: 3.5
       env: TOXENV=py35
+      stage: test
+
     - python: 3.6
       env: TOXENV=py36
+      stage: test
+
+    - python: 3.7
+      env: TOXENV=py37
+      stage: test
+
+    - python: 3.8-dev
+      env: TOXENV=py38
+      stage: test
+
+    - python: nightly
+      env: TOXENV=py38
+      stage: test
+
     - python: pypy
       env: TOXENV=pypy
-    # This should be tested. Problem is, Travis are using Python 3.2 for pypy3 which is no longer supported by pip
-    # - python: pypy3
-    #   env: TOXENV=pypy3
+      stage: test
+
+    - python: pypy3.5
+      env: TOXENV=pypy35
+      stage: test
+
+  allow_failures:
+    - python: 3.8-dev
+    - python: nightly
 
 before_install:
   - pip install codecov

setup.py

@@ -61,6 +61,7 @@ def read(*parts):
         'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
         'Topic :: Software Development :: Libraries :: Python Modules',
         'Topic :: System :: Operating System',
     ]

tests/test_distro.py

@@ -1618,7 +1618,7 @@ def _bad_os_listdir(path='.'):
     raise OSError()
 
 
-@pytest.mark.skipIf(not IS_LINUX, reason='Irrelevant on non-linx')
+@pytest.mark.skipif(not IS_LINUX, reason='Irrelevant on non-linux')
 class TestOverallWithEtcNotReadable(TestOverall):
     def setup_method(self, test_method):
         self._old_listdir = os.listdir

tox.ini

@@ -14,7 +14,7 @@
 
 [tox]
 minversion = 1.7.2
-envlist = flake8, py3flake8, py27, py33, py34, py35, py36, pypy
+envlist = flake8, py3flake8, py27, py3{4,5,6,7,8}, pypy{,35}
 skip_missing_interpreters = true
 
 [testenv]
@@ -37,6 +37,6 @@ deps = flake8
 commands = flake8 distro.py
 
 [testenv:py3flake8]
-basepython = python3.6
+basepython = python3.7
 deps = flake8
 commands = flake8 distro.py