docs: fix simple typo, rumtime -> runtime
docs: fix simple typo, rumtime -> runtime

There is a small typo in libfwupd/fwupd-client.c.

Should read `runtime` rather than `rumtime`.

fwupd/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,hughsie/fwupd,fwupd/fwupd