Update travis configuration

.travis.yml

 # Validate this file using http://lint.travis-ci.org/
+dist: xenial
 language: python
 sudo: false
 cache: pip
@@ -6,7 +7,9 @@ python: "2.7"
 addons:
   apt_packages: swig
   postgresql: "9.4"
-services: redis-server
+services:
+  - redis-server
+  - mysql
 before_install:
   - CFLAGS=-O0 pip install -r requirements.txt
   - pip install psycopg2