Fix deprecation warning about typing.re.Pattern (#194)

https://docs.python.org/3/library/typing.html#typing.Pattern

duniterpy/documents/document.py

@@ -17,8 +17,7 @@ import base64
 import hashlib
 import logging
 import re
-from typing import Any, Dict, Optional, Type, TypeVar
-from typing.re import Pattern
+from typing import Any, Dict, Optional, Pattern, Type, TypeVar
 
 from ..constants import SIGNATURE_REGEX
 from ..key import SigningKey, VerifyingKey