Fixed unittesting with tox
diff --git a/tests/test_strings.py b/tests/test_strings.py
index 001456d..4af0629 100644
--- a/tests/test_strings.py
+++ b/tests/test_strings.py
@@ -6,7 +6,7 @@
 
 import rsa
 
-from tests.constants import unicode_string
+from constants import unicode_string
 
 class StringTest(unittest2.TestCase):