Fixed SQL issue in PGSQL DB Create.

Author: Neil Ferreira

cookbook/configuration/pdo_session_storage.rst

@@ -180,5 +180,5 @@ For PostgreSQL, the statement should look like this:
         session_id character varying(255) NOT NULL,
         session_value text NOT NULL,
         session_time integer NOT NULL,
-        CONSTRAINT session_pkey PRIMARY KEY (session_id),
+        CONSTRAINT session_pkey PRIMARY KEY (session_id)
     );