py-psycopg2: updated to 2.7.6

Psycopg 2.7.6:

Summary of changes:
- Close named cursors if exist, even if execute() wasn't called.
- Fixed building on modern FreeBSD versions with Python 3.7.
- Fixed hang trying to COPY via execute() in asynchronous connections.
- Fixed adaptation of arrays of empty arrays.
- Fixed segfault accessing the connection.readonly and connection.deferrable attributes repeatedly.
- execute_values() accepts sql.Composable objects.
- errorcodes map updated to PostgreSQL 11.
- Wheel package compiled against PostgreSQL 10.5 libpq and OpenSSL 1.0.2p.


(adam)