Travis: test Python 3.7, 3.8

[closes #20]

Squashed commit of the following:

commit 5257fee
Author: Adam Hooper <[email protected]>
Date:   Mon Dec 30 10:55:24 2019 -0500

    Travis: Fix test-dep installation

commit 6239e7e
Author: Adam Hooper <[email protected]>
Date:   Mon Dec 30 10:50:11 2019 -0500

    Another attempt at wrangling Travis

commit 3be9c45
Author: Adam Hooper <[email protected]>
Date:   Mon Dec 30 10:31:30 2019 -0500

    Travis: fix pytest-asyncio installation

commit 2e0e5f2
Author: Adam Hooper <[email protected]>
Date:   Mon Dec 30 10:25:18 2019 -0500

    Travis: test Python 3.7, 3.8

Author: adamhooper

.travis.yml

@@ -4,6 +4,8 @@ language: python
 
 python:
   - "3.6"
+  - "3.7"
+  - "3.8"
 
 services:
   - docker
@@ -26,7 +28,7 @@ script:
   - pyflakes .
   - black --check .
   - isort --check-only --diff --recursive channels_rabbitmq tests
-  - pytest --verbose
+  - pytest -v
 
 deploy:
   provider: pypi

setup.cfg

@@ -19,13 +19,9 @@ line_length=88
 known_first_party = channels, asgiref, channels_rabbitmq
 
 [tox]
-envlist = py36
+envlist = py36, py37, py38
 
 [testenv]
-deps =
-  pytest~=3.6.0
-  pytest-runner
-  pytest-asyncio~=0.8
-  pytest-timeout~=1.3.3
+extras = tests
 commands =
   pytest {posargs}

setup.py

@@ -7,6 +7,8 @@
 # We use the README as the long_description
 readme = open(join(dirname(__file__), "README.rst")).read()
 
+tests_require = ["pytest~=3.6.0", "pytest-asyncio~=0.8", "pytest-timeout~=1.3.3"]
+
 setup(
     name="channels_rabbitmq",
     version=__version__,
@@ -25,5 +27,6 @@
         "msgpack~=0.6.1",
         "channels~=2.2",
     ],
-    tests_require=["pytest~=3.6.0", "pytest-asyncio~=0.8", "pytest-timeout~=1.3.3"],
+    tests_require=tests_require,  # for `python ./setup.py test`
+    extras_require={"tests": tests_require},  # for bare `pytest`
 )