Fix typing of the get_meta_refresh() result (#211)

Also bump mypy and remove --show-error-codes from tox.ini as it's already in 
mypy.ini.

Author: wRAR

tox.ini

@@ -27,9 +27,9 @@ basepython = python3
 deps =
     # mypy would error if pytest (or its sub) not found
     pytest
-    mypy==0.991
+    mypy==1.0.0
 commands =
-    mypy --strict --show-error-codes {posargs: w3lib tests}
+    mypy --strict {posargs: w3lib tests}
 
 [testenv:flake8]
 basepython = python3

w3lib/html.py

@@ -328,8 +328,8 @@ def get_meta_refresh(
     baseurl: str = "",
     encoding: str = "utf-8",
     ignore_tags: Iterable[str] = ("script", "noscript"),
-) -> Tuple[Optional[float], Optional[str]]:
-    """Return  the http-equiv parameter of the HTML meta element from the given
+) -> Union[Tuple[None, None], Tuple[float, str]]:
+    """Return the http-equiv parameter of the HTML meta element from the given
     HTML text and return a tuple ``(interval, url)`` where interval is an integer
     containing the delay in seconds (or zero if not present) and url is a
     string with the absolute url to redirect.