Updating/fixing Travis-CI build

- Dropping Python 3.3 job from Travis build. Adding 3.6,3.7
- Adding services for postgresql and mysql

Author: mwatts15

.travis.yml

@@ -1,15 +1,24 @@
 language: python
+
 env:
 - DB=pgsql
 - DB=mysql
 - DB=sqlite
+
+services:
+- postgresql
+- mysql
+
 python:
 - 2.7
-- 3.3
 - 3.4
 - 3.5
+- 3.6
+- 3.7
+
 install:
 - pip install -U setuptools tox tox-travis
+
 before_script:
 - sh -c "if [ '$DB' = 'pgsql' ]; then psql -c 'DROP DATABASE IF EXISTS test;' -U postgres;
   psql -c 'create database test;' -U postgres; export DBURI='postgresql+psycopg2://postgres@localhost/test';
@@ -18,7 +27,9 @@ before_script:
   export DBURI='mysql+mysqldb://test@localhost/test?charset=utf8'; fi"
 - sh -c "if [ '$DB' = 'sqlite' ]; then export DBURI='sqlite:///%(here)s/test.sqlite';
   fi"
+
 script: tox
+
 deploy:
   distributions: sdist bdist_wheel
   provider: pypi