Fix Python scripts on Ubuntu 20.04

Python 3.8 shipped with Ubuntu 20.04 does not support using concrete
types subscript in type hints, e.g. `list[Version]` caused `TypeError:
'type' object is not subscriptable`. This patch fixes #1625 by using the
type hint classes provided by the typing module instead of concrete
types.

Author: kbenzie

scripts/parse_specs.py

@@ -17,7 +17,7 @@
 from templates.helper import param_traits, type_traits, value_traits
 import ctypes
 import itertools
-from typing import Optional
+from typing import Dict, List, Optional
 from version import Version
 
 
@@ -504,7 +504,7 @@ def __validate_union_tag(d):
 """
     filters object by version
 """
-def _filter_version(d, max_ver: Version) -> Optional[dict]:
+def _filter_version(d, max_ver: Version) -> Optional[Dict]:
     ver = Version(d.get('version', default_version))
     if ver > max_ver:
         return None
@@ -550,7 +550,7 @@ def __filter_desc(d) -> dict:
 """
     creates docs per version
 """
-def _make_versions(d, max_ver : Version) -> list[Version]:
+def _make_versions(d, max_ver : Version) -> List[Version]:
     docs = []
     type = d['type']
     if 'function' == type or 'struct' == type: