Make Python 3.7 the default environment for builds/tests.

.travis.yml

@@ -22,17 +22,17 @@ matrix:
       env: TOXENV=py36-django22
     - python: 3.7
       env: TOXENV=py37-django22
-    - python: 3.6
-      env: TOXENV=py36-djangomaster
+    - python: 3.7
+      env: TOXENV=py37-djangomaster
 
-    - python: 3.6
+    - python: 3.7
       env: TOXENV=lint
-    - python: 3.5
+    - python: 3.7
       env: TOXENV=sandbox
     - python: 3.7
       env: TOXENV=docs
   allow_failures:
-    - env: TOXENV=py36-djangomaster
+    - env: TOXENV=py37-djangomaster
 
 branches:
   only:

Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.5
+FROM python:3.7
 ENV PYTHONUNBUFFERED 1
 
 RUN curl -sL https://deb.nodesource.com/setup_12.x | bash -

docs/source/internals/contributing/running-tests.rst

@@ -8,7 +8,7 @@ Testing requirements
 You'll need:
 
 - A running SQL server (PostgreSQL, or SQLite with `--sqlite` parameters)
-- python3.5 or python3.6
+- python3.6 or python3.7
 
 Running tests
 -------------

tox.ini

@@ -24,7 +24,7 @@ commands =
 
 
 [testenv:lint]
-basepython = python3.6
+basepython = python3.7
 deps =
     flake8
     isort
@@ -37,7 +37,7 @@ commands =
 
 
 [testenv:sandbox]
-basepython = python3.5
+basepython = python3.7
 deps =
     -r{toxinidir}/requirements.txt
     django>=2.2,<2.3