Fixing import.py for python 3

Util/BuildTools/Import.py

@@ -363,7 +363,7 @@ def import_assets(package_name, json_dirname, props, maps, do_tiles, tile_size,
         for umap in maps:
             # import groups of tiles to prevent unreal from using too much memory
             map_template = {}
-            for key, value in umap.iteritems():
+            for key, value in iter(umap.items()):
                 if key is not 'tiles':
                     map_template[key] = value
             map_template['tiles'] = []