lavf/segment: set EXT-X-VERSION to 3 rather than to 4

There is nothing we use of the latest version, downgrade version number
to increase decoding support.

Based on this comment by vel2000:
http://ffmpeg.org/trac/ffmpeg/ticket/1642#comment:17

libavformat/segment.c

@@ -127,7 +127,7 @@ static int segment_list_open(AVFormatContext *s)
 
     if (seg->list_type == LIST_TYPE_M3U8) {
         avio_printf(seg->list_pb, "#EXTM3U\n");
-        avio_printf(seg->list_pb, "#EXT-X-VERSION:4\n");
+        avio_printf(seg->list_pb, "#EXT-X-VERSION:3\n");
     }
 
     return ret;