docs: Fix a trivial typo in GMount documentation
docs: Fix a trivial typo in GMount documentation

Signed-off-by: Philip Withnall <29c2a2ac2a854b9cf047275aa9de346d096be2e0@endlessm.com>

johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib