fix: correct type hint for Matrix.durations (#132)

Author: mthh

routingpy/matrix.py

@@ -31,7 +31,7 @@ def __init__(self, durations=None, distances=None, raw=None):
         self._raw = raw
 
     @property
-    def durations(self) -> Optional[List[List[float]]]:
+    def durations(self) -> Optional[List[List[Optional[float]]]]:
         """
         The durations matrix as list akin to::