update changelog [ci skip]

Author: kripken

ChangeLog.md

@@ -21,6 +21,7 @@ Current Trunk
   use `requestFullscreen` (without the capital S).
 - Remove deprecated `requestFullScreen` and `cancelFullScreen` from `library_glut.js`
 - Remove deprecated `requestFullScreen` and `cancelFullScreen`from `library_glfw.js`
+- Fix SDL2_mixer support for ogg vorbis. See #9849
 
 v1.39.3: 11/14/2019
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