Fix TypeError: 'type' object is not subscriptable if using python ver…

…sions 3.7 or 3.8

sa_filters/pagination.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 import math
 from collections import namedtuple
+import sys
 from typing import Optional, Union
 
 from sqlalchemy.sql import Select
@@ -9,6 +10,12 @@
 from .exceptions import InvalidPage
 
 
+if sys.version_info < (3, 9):  # pragma: nocover
+    from typing import Tuple as TupleType
+else:  # pragma: nocover
+    TupleType = tuple
+
+
 Pagination = namedtuple(
     'Pagination', ['page_number', 'page_size', 'num_pages', 'total_results']
 )
@@ -19,7 +26,7 @@ def apply_pagination(
         page_number: Optional[int] = None,
         page_size: Optional[int] = None,
         total_results: int = 0
-) -> tuple[Union[Select, Query], Pagination]:
+) -> TupleType[Union[Select, Query], Pagination]:
     """Apply pagination to a SQLAlchemy query or Select object.
 
     :param stmt: