Fix circular import issue (#894)

Author: ZackAttack614

hexrd/hedm/config/__init__.py

@@ -15,7 +15,7 @@
 open_file = open
 
 
-def open(file_name=None) -> list[root.RootConfig]:
+def open(file_name=None) -> list['root.RootConfig']:
     """
     Reads configuration settings from a yaml file.