flashsv2enc: mark encoder experimental

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/flashsv2enc.c

@@ -903,4 +903,5 @@ AVCodec ff_flashsv2_encoder = {
     flashsv2_encode_end,
     .pix_fmts = (enum PixelFormat[]) {PIX_FMT_BGR24, PIX_FMT_NONE},
     .long_name = NULL_IF_CONFIG_SMALL("Flash Screen Video Version 2"),
+    .capabilities   =  CODEC_CAP_EXPERIMENTAL,
 };