Allow psycopg 2.7 to make Travis green again

stefano-maggiolo · lw · commit cf5b0968edd2 · 2018-01-28T14:18:15.000+01:00
Cherry-picked from d5211c0.
diff --git a/requirements.txt b/requirements.txt
@@ -1,5 +1,5 @@
 tornado==4.1
-psycopg2==2.6
+psycopg2>=2.6,<2.8
 sqlalchemy>=0.9,<1.1
 netifaces==0.10.4
 pycrypto==2.6.1
