Install black in travis yaml

Author: jordaneb

.travis.yml

@@ -16,6 +16,7 @@ env:
 install:
 - pip install -r test-requirements.txt
 - pip install -U django==$DJANGO_VERSION
+- if [ "$TRAVIS_PYTHON_VERSION" != "3.5" ]; then pip install black==19.10b0; fi
 script:
   - if [ "$TRAVIS_PYTHON_VERSION" != "3.5" ]; then black --check django_dbq; fi
   - python manage.py test

test-requirements.txt

@@ -1,5 +1,4 @@
 -r requirements.txt
-black==19.10b0
 mysqlclient==1.4.6
 freezegun==0.3.12
 mock==3.0.5