Add Django 2.0/2.1 support & drop Django 1.8 support

docs/source/quickstart.rst

@@ -13,9 +13,10 @@ Python
 
 Supported Frameworks
 ^^^^^^^^^^^^^^^^^^^^
-* Django 1.8
 * Django 1.11
 * Django 2.0
+* Django 2.1
+* Django 2.2
 
 Installation
 ------------

tox.ini

@@ -2,29 +2,30 @@
 envlist =
     py27, py35, py36, py37, py38,
     ; https://docs.djangoproject.com/en/dev/faq/install/#what-python-version-can-i-use-with-django
-    py27-django{18,111},
-    py35-django{111,20},
-    py36-django{111,20},
-    py37-django{111,20},
+    py27-django111,
+    py35-django{111,20,21,22},
+    py36-django{111,20,21,22},
+    py37-django{111,20,21,22},
     coverage, docs, flake8, mypy
 
 [travis]
 python =
-    2.7: py27, py27-django{18,111}, coverage, docs, flake8
-    3.5: py35, py35-django{111,20}, coverage, docs
-    3.6: py36, py36-django{111,20}
-    3.7: py37, py37-django{111,20}
+    2.7: py27, py27-django111, coverage, docs, flake8
+    3.5: py35, py35-django{111,20,21,22}, coverage, docs
+    3.6: py36, py36-django{111,20,21,22}
+    3.7: py37, py37-django{111,20,21,22}
     3.8: py38, flake8, mypy
 
 [testenv]
 deps =
-    django18: Django>=1.8,<1.9
     django111: Django>=1.11,<1.12
     django20: Django>=2.0,<2.1
+    django21: Django>=2.1,<2.2
+    django22: Django>=2.2,<2.3
 commands =
     pip install -e .[test]
     pytest tests/core
-    django{18,111,20}: python tests/django/runtests.py
+    django{111,20,21,22}: python tests/django/runtests.py
 passenv = CHANNELS_* TRAVIS TRAVIS_BRANCH TRAVIS_JOB_ID
 
 [testenv:coverage]