Support mypy v0.990 new Optional report

• PEP 484 prohibits implicit Optional
• Bump pre-commit hooks

duniterpy/api/bma/blockchain.py

@@ -15,7 +15,7 @@
 
 import logging
 from http.client import HTTPResponse
-from typing import Union
+from typing import Optional, Union
 
 from duniterpy.api.client import RESPONSE_HTTP, Client
 
@@ -266,7 +266,10 @@ def current(client: Client) -> dict:
 
 
 def block(
-    client: Client, number: int = 0, block_raw: str = None, signature: str = None
+    client: Client,
+    number: int = 0,
+    block_raw: Optional[str] = None,
+    signature: Optional[str] = None,
 ) -> Union[dict, HTTPResponse]:
     """
     GET/POST a block from/to the blockchain