Rename parameter to match the actual name in stdlib (#1959)

Author: passichenko

stdlib/3.4/asyncio/events.pyi

@@ -88,7 +88,7 @@ class AbstractEventLoop(metaclass=ABCMeta):
     @abstractmethod
     @coroutine
     def run_in_executor(self, executor: Any,
-        callback: Callable[..., _T], *args: Any) -> Generator[Any, None, _T]: ...
+        func: Callable[..., _T], *args: Any) -> Generator[Any, None, _T]: ...
     @abstractmethod
     def set_default_executor(self, executor: Any) -> None: ...
     # Network I/O methods returning Futures.