Make Python 3.6 friendly

src/ansi_string/ansi_string.py

@@ -1030,7 +1030,7 @@ def __str__(self) -> str:
         return self.__format__(None)
 
     @staticmethod
-    def _re_search(expr:Union[str, "re.Pattern[str]"], string:str, result:List[re.Match[str]]) -> Union[re.Match[str], None]:
+    def _re_search(expr:Union[str, "re.Pattern[str]"], string:str, result:List["re.Match[str]"]) -> Union["re.Match[str]", None]:
         '''
         Helper method so I can assign and check in the same "if" statement
         '''