Add Django 3.1 to test matrix

Author: AlexHill

.travis.yml

@@ -15,6 +15,7 @@ templates:
   django21: &django21 DJANGO_VERSION=2.1.*
   django22: &django22 DJANGO_VERSION=2.2.*
   django30: &django30 DJANGO_VERSION=3.0.*
+  django31: &django31 DJANGO_VERSION=3.1.*
   djangomaster: &djangomaster DJANGO_VERSION=master
 
   postgres: &postgres DATABASE_URL=postgres://postgres@/django_relativity
@@ -49,6 +50,9 @@ matrix:
     - { python: pypy3, env: [*django30, *postgres], <<: *pgdb}
     - { python: pypy3, env: [*django30, *mysql], <<: *mariadb}
     - { python: pypy3, env: [*django30, *sqlite]}
+    - { python: pypy3, env: [*django31, *postgres], <<: *pgdb}
+    - { python: pypy3, env: [*django31, *mysql], <<: *mariadb}
+    - { python: pypy3, env: [*django31, *sqlite]}
     - { python: pypy3, env: [*djangomaster, *postgres], <<: *pgdb}
     - { python: pypy3, env: [*djangomaster, *mysql], <<: *mariadb}
     - { python: pypy3, env: [*djangomaster, *sqlite]}
@@ -90,6 +94,9 @@ matrix:
     - { python: 3.6, env: [*django30, *postgres], <<: *pgdb}
     - { python: 3.6, env: [*django30, *mysql], <<: *mariadb}
     - { python: 3.6, env: [*django30, *sqlite]}
+    - { python: 3.6, env: [*django31, *postgres], <<: *pgdb}
+    - { python: 3.6, env: [*django31, *mysql], <<: *mariadb}
+    - { python: 3.6, env: [*django31, *sqlite]}
     - { python: 3.6, env: [*djangomaster, *postgres], <<: *pgdb}
     - { python: 3.6, env: [*djangomaster, *mysql], <<: *mariadb}
     - { python: 3.6, env: [*djangomaster, *sqlite]}
@@ -109,6 +116,9 @@ matrix:
     - { python: 3.7, env: [*django30, *postgres], <<: *pgdb}
     - { python: 3.7, env: [*django30, *mysql], <<: *mariadb}
     - { python: 3.7, env: [*django30, *sqlite]}
+    - { python: 3.7, env: [*django31, *postgres], <<: *pgdb}
+    - { python: 3.7, env: [*django31, *mysql], <<: *mariadb}
+    - { python: 3.7, env: [*django31, *sqlite]}
     - { python: 3.7, env: [*djangomaster, *postgres], <<: *pgdb}
     - { python: 3.7, env: [*djangomaster, *mysql], <<: *mariadb}
     - { python: 3.7, env: [*djangomaster, *sqlite]}
@@ -119,6 +129,9 @@ matrix:
     - { python: 3.8, env: [*django30, *postgres], <<: *pgdb}
     - { python: 3.8, env: [*django30, *mysql], <<: *mariadb}
     - { python: 3.8, env: [*django30, *sqlite]}
+    - { python: 3.8, env: [*django31, *postgres], <<: *pgdb}
+    - { python: 3.8, env: [*django31, *mysql], <<: *mariadb}
+    - { python: 3.8, env: [*django31, *sqlite]}
     - { python: 3.8, env: [*djangomaster, *postgres], <<: *pgdb}
     - { python: 3.8, env: [*djangomaster, *mysql], <<: *mariadb}
     - { python: 3.8, env: [*djangomaster, *sqlite]}
@@ -130,7 +143,6 @@ matrix:
 
 
 install:
-  - bash -c "echo $TRAVIS_PYTHON_VERSION"
   - pip install -r test-requirements.txt
   - bash -c "if [[ $DATABASE_URL = postgres* ]] && [[ $TRAVIS_PYTHON_VERSION == pypy* ]]; then pip install psycopg2cffi; fi;"
   - bash -c "if [[ $DATABASE_URL = postgres* ]] && [[ $TRAVIS_PYTHON_VERSION != pypy* ]]; then pip install psycopg2-binary; fi;"