trivial: Fix up a small gtk-doc issue
trivial: Fix up a small gtk-doc issue

cgwalters/libhif,Conan-Kudo/libhif,hughsie/libhif,rpm-software-management/libdnf,rpm-software-management/libhif,juhp/libhif,edynox/libdnf,cgwalters/libhif,rpm-software-management/libhif,rpm-software-management/libhif,edynox/libdnf,juhp/libhif,Conan-Kudo/libhif,Conan-Kudo/libhif,rpm-software-management/libdnf,hughsie/libhif,edynox/libdnf,rpm-software-management/libdnf,kalev/libhif,cgwalters/libhif,rpm-software-management/libdnf,kalev/libhif,Conan-Kudo/libhif,cgwalters/libhif,hughsie/libhif,rpm-software-management/libhif,hughsie/libhif,edynox/libdnf