add missing modifyHook for watcher

Needed for FSEvents, which calls that hook for modified files.
inotify seems to call the add hook, so I didn't notice it before.

Assistant/Threads/Watcher.hs

@@ -69,6 +69,7 @@ watchThread = NamedThread "Watcher" $ do
 	errhook <- hook onErr
 	let hooks = mkWatchHooks
 		{ addHook = addhook
+		, modifyHook = addhook
 		, delHook = delhook
 		, addSymlinkHook = addsymlinkhook
 		, delDirHook = deldirhook