Fixed pep8 error
diff --git a/tests/hazmat/primitives/test_hkdf.py b/tests/hazmat/primitives/test_hkdf.py
index 3dea3f2..42c75c6 100644
--- a/tests/hazmat/primitives/test_hkdf.py
+++ b/tests/hazmat/primitives/test_hkdf.py
@@ -17,7 +17,9 @@
 
 import pytest
 
-from cryptography.exceptions import AlreadyFinalized, InvalidKey, UnsupportedInterface
+from cryptography.exceptions import (
+    AlreadyFinalized, InvalidKey, UnsupportedInterface)
+
 from cryptography.hazmat.primitives import hashes
 from cryptography.hazmat.primitives.kdf.hkdf import HKDF