RotatingFileHandler has a terminator property (#1952)

In python3 `RotatingFileHandler` is a subclass of `BaseRotatingHandler` which is a subclass of `FileHandler` which is a subclass of `StreamHandler` which as a `terminator` property but I'm getting a `"RotatingFileHandler" has no attribute "terminator"` error on my code.

Author: jmcs

stdlib/2and3/logging/handlers.pyi

@@ -29,6 +29,7 @@ class WatchedFileHandler(Handler):
 
 if sys.version_info >= (3,):
     class BaseRotatingHandler(FileHandler):
+        terminator = ...  # type: str
         namer = ...  # type: Optional[Callable[[str], str]]
         rotator = ...  # type: Optional[Callable[[str, str], None]]
         def __init__(self, filename: str, mode: str,