Correct spelling of spawn_async_with_pipes() in doc comment
Fix spelling of spawn_async_with_pipes() as published here:
https://developer.gnome.org/glibmm/stable/group__Spawn.html#ga68ea12be3693ed49e92312b63bef2d38
"The caller of pawn_async_with_pipes() must close these" ...
Edited by Mike Fleetwood