Use the us depot for sea maps.

It seems as though sea doesn't have its own depot. This will probably
affect s2gs files as well. We've not yet confirmed.

Author: GraylinKim

sc2reader/resources.py

@@ -602,6 +602,8 @@ def __init__(self, map_file, filename=None, gateway=None, map_hash=None, **optio
     def get_url(cls, gateway, map_hash):
         """Builds a download URL for the map from its components."""
         if gateway and map_hash:
+            # it seems like sea maps are stored on us depots.
+            gateway = 'us' if gateway=='sea' else gateway
             return cls.url_template.format(gateway, map_hash)
         else:
             return None