Changelog: replace <next> by 4.4

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

Changelog

 Entries are sorted chronologically from oldest to youngest within each release,
 releases are sorted from youngest to oldest.
 
-version <next>:
+version 4.4:
 - AudioToolbox output device
 - MacCaption demuxer
 - PGX decoder