Bumped psycopg2 hoping to fix jsonb errors in CI

requirements.txt

@@ -15,7 +15,7 @@ ncclient==0.5.3
 netaddr==0.7.18
 paramiko>=2.0.0
 Pillow>=4.0.0
-psycopg2>=2.6.1
+psycopg2>=2.7.3
 py-gfm>=0.1.3
 pycrypto>=2.6.1
 sqlparse>=0.2