Update Python versions in Travis CI and tox (#1902)

- run lint using latest Python 3.7
- updated env list in tox.ini
  - added py38-dev
  - removed py36-dev
- moved aiohttp to requirements_test.txt

Signed-off-by: Brett Randall <javabrett@gmail.com>

.travis.yml

@@ -2,8 +2,10 @@ sudo: false
 language: python
 matrix:
   include:
-    - python: 3.6
+    - python: 3.7
       env: TOXENV=lint
+      dist: xenial
+      sudo: true
     - python: 3.4
       env: TOXENV=py34
     - python: 3.5

requirements_test.txt

@@ -1,3 +1,4 @@
+aiohttp
 coverage>=4.0,<4.4  # TODO: https://github.com/benoitc/gunicorn/issues/1548
 pytest
 pytest-cov==2.5.1

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py34, py35, py36, py36-dev, py37, pypy, lint
+envlist = py34, py35, py36, py37, py38-dev, pypy, lint
 skipsdist = True
 
 [testenv]
@@ -7,7 +7,6 @@ usedevelop = True
 commands = py.test {posargs}
 deps =
   -rrequirements_test.txt
-  py{34,35,36,36-dev,37}: aiohttp
 
 [testenv:lint]
 commands =