try loading psycopg2 for python 2

Looks like psycopg2 pip install was removed.
No obvious reason for its deletion in the logs.

no-github-ci as this affects travis only.

Author: rouilj

.travis.yml

@@ -132,6 +132,7 @@ install:
   - pip install redis
   - pip install pytz whoosh pyjwt requests
   - pip install jinja2
+  - pip install psycopg2
   # note pytest-env is not needed for redis password as there is
   # no password on CI's redis.
   - pip install pytest-cov