webp-lossless-bitstream-spec: fix BNF
webp-lossless-bitstream-spec: fix BNF

color cache info precedes the meta huffman info

Bug: webp:551
Change-Id: Ibb69b4ffad6bff5693015be3fe6c600c53fd06c0

webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp,webmproject/libwebp