Fix tests on py26

the print() function does not appear to be mockable there

letsencrypt/tests/hook_test.py

@@ -3,6 +3,7 @@
 
 import os
 import unittest
+import sys
 
 import mock
 
@@ -76,8 +77,12 @@ class HookTest(unittest.TestCase):
             self.assertEqual(os.environ["RENEWED_DOMAINS"], "a b")
             self.assertEqual(os.environ["RENEWED_LINEAGE"], "thing")
 
-            with mock.patch("letsencrypt.hooks.print") as mock_print:
             config = mock.MagicMock(renew_hook="true", dry_run=True)
+            if sys.version_info < (2, 7):
+                # the print() function is not mockable in py26
+                self._test_a_hook(config, rhook, 0)
+            else:
+                with mock.patch("letsencrypt.hooks.print") as mock_print:
                     self._test_a_hook(config, rhook, 0)
                     self.assertEqual(mock_print.call_count, 2)