python: Reformat with Black, except quotes.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/lib/timezone.py

@@ -17,9 +17,11 @@ def get_canonical_timezone_map() -> Dict[str, str]:
                 canonical[alias] = name
     return canonical
 
+
 def canonicalize_timezone(key: str) -> str:
     return get_canonical_timezone_map().get(key, key)
 
+
 # Note: some of these abbreviations are fundamentally ambiguous (see
 # zerver/tests/test_timezone.py), so you should never rely on them as
 # anything more than a heuristic.