fix: bump minimum cryptography dependency to >= 39.0.0

The  kwarg used in jwk.py lines 842
and 1000 was added to cryptography in version 39.0.0 (PR #7667).

Without this bump, pip can install jwcrypto 1.5.7 with cryptography
< 39.0.0, causing:

  TypeError: load_pem_private_key() got an unexpected keyword argument
  'unsafe_skip_rsa_key_validation'

Fixes #376

Author: xyaz1313

pyproject.toml

@@ -22,7 +22,7 @@ classifiers = [
     "Topic :: Software Development :: Libraries :: Python Modules",
 ]
 dependencies = [
-    "cryptography >= 3.4",
+    "cryptography >= 39.0.0",
     "typing_extensions >= 4.5.0",
 ]