[CSS21] Typos in Section 15.3.1.1 serif

Find 15.3.1.1 serif

Replace: 


Cyrillic fonts 

Adobe Minion Cyrillic, Excelcior Cyrillic Upright, Monotype Albion 70,
Bitstream Cyberbit, ER Bukinst 

With: 


Cyrillic fonts 

Adobe Minion Cyrillic, Excelsior Cyrillic Upright, Monotype Albion 70,
Bitstream Cyberbit, ER Bukinist 

These errors are harmful; the list gets repeated all over the place (Web).