updated .travis.yml

.travis.yml

@@ -16,12 +16,15 @@ install:
   - pip install -r conf/requirements-dev.txt
   - pip install coveralls
 
-before_script:
-  - sudo apt-get install postgresql-9.6-postgis-2.3 postgis -y -q
-
 script:
   - cd tests/testapp/
   - coverage run --source='../../mapwidgets' manage.py test
 
 after_success:
   - coveralls
+
+addons:
+  postgresql: 9.6
+  apt:
+    packages:
+    - postgresql-9.6-postgis-2.3