MAINTAINERS: add 2.8, drop 2.2

No actively maintained linux disto on
https://trac.ffmpeg.org/wiki/Downstreams
uses 2.2 anymore, so it makes no sense to maintain it further

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

MAINTAINERS

@@ -564,11 +564,11 @@ x86                                     Michael Niedermayer
 Releases
 ========
 
+2.8                                     Michael Niedermayer
 2.7                                     Michael Niedermayer
 2.6                                     Michael Niedermayer
 2.5                                     Michael Niedermayer
 2.4                                     Michael Niedermayer
-2.2                                     Michael Niedermayer
 
 If you want to maintain an older release, please contact us