Add video/x-matroska with extension mkv

Author: punkrats

lib/mime/types/video.nonstandard

@@ -4,6 +4,7 @@ video/x-fli @fli :base64
 video/x-flv @flv :base64
 video/x-gl @gl :base64
 video/x-ivf @ivf
+video/x-matroska @mkv
 video/x-motion-jpeg @mjpg
 video/x-ms-asf @asf,asx
 video/x-ms-wm @wm