Fix typeshed def for Popen.kill() and Popen.terminate()

Author: Peter Amstutz

typeshed/2.7/subprocess32.pyi

@@ -49,5 +49,5 @@ class Popen:
     def poll(self) -> int: ...
     def wait(self, timeout: Optional[Any] = ..., endtime: Optional[Any] = ...): ...
     def send_signal(self, sig): ...
-    def terminate(self): ...
-    def kill(self): ...
+    def terminate(self) -> None: ...
+    def kill(self) -> None: ...