enc/vp8enci.h: update version number

0.4.1 -> 0.4.2
missed in: 857578a bump version to 0.4.2

Change-Id: Iaa62ce5af5935243748e51105008f252443e7d27
update ChangeLog

Change-Id: Ib9504997d00c9f72cff30aa699fe1998b6be940d