fix format string to work on py26

Michael Merickel

2016-04-16 dd45cf8171c0ab08afa7529a3841c67c1fc01a02

fix format string to work on py26

 pyramid/session.py

@@ -192,7 +192,7 @@
        if not any(is_same_domain(originp.netloc, host)
                   for host in trusted_origins):
            reason = (
                "Referer checking failed - {} does not match any trusted "
                "Referer checking failed - {0} does not match any trusted "
                "origins."
            )
            return _fail(reason.format(origin))