Why my customized snippets can't take effect?

[hwypengsir]

webapi-vim has been installed in bundle:

cd  ~/.vim/bundle
git clone https://github.com/mattn/webapi-vim
ls  
emmet-vim  ultisnips  vim-snippets  webapi-vim

Add g:user_emmet_settings in .vimrc:

let g:user_emmet_settings = webapi#json#decode(join(readfile(expand('/home/debian/.vim/bundle/emmet-vim/snippets.json')), "\n"))

Edit the snippets.json:

cat  /home/debian/.vim/bundle/emmet-vim/snippets.json
{
    "html": {
        "abbreviations": {
            "hello": "testing abbreviation"
        }
    }
}

hello expand into <hello></hello> when edit html file instead of testing abbreviation,how to fix it?