fix bug in build_meta for values that are already list types (like requires_machine)

wozardry

@@ -394,6 +394,8 @@ class WozWriter(WozValidator):
         for key, value_raw in self.meta.items():
             if type(value_raw) == str:
                 values = [value_raw]
+            else:
+                values = value_raw
             list(map(self.validate_metadata_value, values))
             if key == "language":
                 list(map(self.validate_metadata_language, values))