Bump psycopg2 from 2.7 to 2.7.5

Bumps [psycopg2](https://github.com/psycopg/psycopg2) from 2.7 to 2.7.5.
- [Release notes](https://github.com/psycopg/psycopg2/releases)
- [Changelog](https://github.com/psycopg/psycopg2/blob/master/NEWS)
- [Commits](https://github.com/psycopg/psycopg2/commits)

Signed-off-by: dependabot[bot] <support@dependabot.com>

test-requirements.txt

@@ -7,4 +7,4 @@ celery==3.1.25
 django-celery==3.2.2
 flake8==3.2.1
 requests==2.18.4
-psycopg2==2.7
+psycopg2==2.7.5