fix: correct type hint for Matrix.distances

following up on d8c9bf6 / #132

Author: mthh

routingpy/matrix.py

@@ -56,7 +56,7 @@ def durations(self) -> Optional[List[List[Optional[float]]]]:
         return self._durations
 
     @property
-    def distances(self) -> Optional[List[List[float]]]:
+    def distances(self) -> Optional[List[List[Optional[float]]]]:
         """
         The distance matrix as list akin to::