trivial: contrib/setup: update markdown if it's too old
trivial: contrib/setup: update markdown if it's too old

gi-docgen requires 3.3.3 or later, but some of the distro packages
are too old.  Upgrade them to make the default

```
meson build
```

work out of the box

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