optparse: option_class is Type[Option] (python#4338)

It's a `class`, not an `instance`.

<https://docs.python.org/2.7/library/optparse.html#optparse.OptionParser>

stdlib/2and3/optparse.pyi

@@ -1,6 +1,6 @@
 # Generated by pytype, with only minor tweaks. Might be incomplete.
 import sys
-from typing import IO, Any, AnyStr, Callable, Dict, Iterable, List, Mapping, Optional, Sequence, Tuple, Union, overload
+from typing import IO, Any, AnyStr, Callable, Dict, Iterable, List, Mapping, Optional, Sequence, Tuple, Type, Union, overload
 
 # See https://groups.google.com/forum/#!topic/python-ideas/gA1gdj3RZ5g
 if sys.version_info >= (3,):
@@ -125,8 +125,8 @@ class OptionContainer:
     conflict_handler: _Text
     defaults: Dict[_Text, Any]
     description: Any
-    option_class: Any
-    def __init__(self, option_class: Option, conflict_handler: Any, description: Any) -> None: ...
+    option_class: Type[Option]
+    def __init__(self, option_class: Type[Option], conflict_handler: Any, description: Any) -> None: ...
     def _check_conflict(self, option: Any) -> None: ...
     def _create_option_mappings(self) -> None: ...
     def _share_option_mappings(self, parser: OptionParser) -> None: ...
@@ -183,7 +183,7 @@ class OptionParser(OptionContainer):
         self,
         usage: Optional[_Text] = ...,
         option_list: Iterable[Option] = ...,
-        option_class: Option = ...,
+        option_class: Type[Option] = ...,
         version: Optional[_Text] = ...,
         conflict_handler: _Text = ...,
         description: Optional[_Text] = ...,