CommitMessageVerificationTest: fix DeprecationWarning for assertRegexpMatches

Signed-off-by: Zac Medico <zmedico@gentoo.org>
diff --git a/repoman/lib/repoman/tests/commit/test_commitmsg.py b/repoman/lib/repoman/tests/commit/test_commitmsg.py
index a734c10..83fa0f3 100644
--- a/repoman/lib/repoman/tests/commit/test_commitmsg.py
+++ b/repoman/lib/repoman/tests/commit/test_commitmsg.py
@@ -29,7 +29,7 @@
 Expected: /%s/
 Errors:
 %s''' % (commitmsg, reason_re, expl))
-		self.assertRegexpMatches(expl, reason_re,
+		(self.assertRegex if hasattr(self, 'assertRegex') else self.assertRegexpMatches)(expl, reason_re,
 				'''Commit message verification did not return expected error, for:
 %s