fixed mypy spurious warning on python 3.6
@@ -140,7 +140,8 @@ class BlockHeader:
dict_["version"],
dict_["previous_block_hash"],
dict_["merkle_root"],
- datetime.fromisoformat(dict_["time"]),
+ # mypy with python 3.6 complain about the following
+ datetime.fromisoformat(dict_["time"]), # type: ignore
dict_["bits"],
dict_["nonce"],
check_validity,
