Ensure box remove uses force (#99)

Author: ssbarnea

vagrant/__init__.py

@@ -838,7 +838,7 @@ def box_remove(self, name, provider):
         Removes the box matching name and provider. It is an error if no box
         matches name and provider.
         """
-        self._call_vagrant_command(["box", "remove", name, provider])
+        self._call_vagrant_command(["box", "remove", "--force", name, provider])
 
     def plugin_list(self):
         """