Change public_key from abstractproperty to abstractmethod
diff --git a/cryptography/hazmat/primitives/interfaces.py b/cryptography/hazmat/primitives/interfaces.py
index 663f965..3d345a9 100644
--- a/cryptography/hazmat/primitives/interfaces.py
+++ b/cryptography/hazmat/primitives/interfaces.py
@@ -371,7 +371,7 @@
         The private key in the DSA structure.
         """
 
-    @abc.abstractproperty
+    @abc.abstractmethod
     def public_key(self):
         """
         The DSAPublicKey associated with this private key.