[css-text-decor] Mongolian Horizontal Preferred position is wrong

The Mongolian Horizontal Preferred position is wrong, it should be under. Like this: 
and Verticla is good : 
Preferred emphasis mark and ruby position
| Language | Preferred position | Illustration |
| Horizontal | Vertical |
| Japanese | over | right | | |
| Korean |
| Mongolian |
| Chinese | under | right | |