Add django-3 to test matrix

Author: last-partizan

.travis.yml

@@ -9,12 +9,13 @@ python:
 env:
   - DJANGO="Django>=1.11,<2.0"
   - DJANGO="Django>=2.0,<2.3"
+  - DJANGO="Django>=3.0,<3.1"
 matrix:
   exclude:
     - python: "2.7"
-      env: DJANGO="Django>=2.0,<2.3"
+      env: DJANGO="Django>=2.0,<2.3" DJANGO="Django>=3.0,<3.1"
     - python: "pypy"
-      env: DJANGO="Django>=2.0,<2.3"
+      env: DJANGO="Django>=2.0,<2.3" DJANGO="Django>=3.0,<3.1"
 before_install:
   - pip install poetry
 install: