Fix function used for Friends.ActivateGameOverlayToStore

[DaFluffyPotato]

I was getting a crash when trying to use Friends.ActivateGameOverlayToStore().

  File "[...]\steamworks\interfaces\friends.py", line 132, in ActivateGameOverlayToStore
    self.steam.ActivateGameOverlayToWebPage(app_id)
ctypes.ArgumentError: argument 1: TypeError: wrong type

It looks like the function was mapped incorrectly in interfaces/friends.py. Changing to the matching function fixed the issue for me.