explicit tox matrix to enable allowed failures

Author: n2ygk

.travis.yml

@@ -3,17 +3,52 @@ dist: bionic
 
 language: python
 
-python:
-  - "3.8"
-  - "3.7"
-  - "3.6"
-  - "3.5"
-
 cache:
   directories:
     - $HOME/.cache/pip
     - $TRAVIS_BUILD_DIR/.tox
 
+# Make sure to coordinate changes to envlist in tox.ini.
+matrix:
+  allow_failures:
+    - env: TOXENV=py36-djangomaster
+    - env: TOXENV=py37-djangomaster      
+    - env: TOXENV=py38-djangomaster
+
+  include:
+    - python: 3.7
+      env: TOXENV=py37-flake8
+    - python: 3.7
+      env: TOXENV=py37-docs
+
+    - python: 3.8
+      env: TOXENV=py38-django30
+    - python: 3.8
+      env: TOXENV=py38-django22
+    - python: 3.8
+      env: TOXENV=py38-django21
+    - python: 3.8
+      env: TOXENV=py38-djangomaster
+
+    - python: 3.7
+      env: TOXENV=py37-django30
+    - python: 3.7
+      env: TOXENV=py37-django22
+    - python: 3.7
+      env: TOXENV=py37-django21
+    - python: 3.7
+      env: TOXENV=py37-djangomaster
+
+    - python: 3.6
+      env: TOXENV=py36-django22
+    - python: 3.6
+      env: TOXENV=py36-django21
+
+    - python: 3.5
+      env: TOXENV=py35-django22
+    - python: 3.5
+      env: TOXENV=py35-django21
+
 install:
   - pip install coveralls tox tox-travis