Merge pull request #525 from AmbientLighter/patch-1

Specify minimal version for cryptography package

Reference:
https://cryptography.io/en/latest/hazmat/primitives/asymmetric/rsa/#cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey.sign

Author: c00kiemon5ter

setup.cfg

@@ -48,7 +48,7 @@ scripts =
     tools/merge_metadata.py
     tools/parse_xsd2.py
 install_requires =
-    cryptography
+    cryptography >= 1.4
     defusedxml
     future
     pyOpenSSL