update nvim nightly bash script

update-nvim.sh

update-nvim () {
    target=${1:-nightly}
    tmp_bin=/tmp/nvim.appimage.${target}
    previous=$(nvim --version|grep '^NVIM')
    url="https://github.com/neovim/neovim/releases/download/${target}/nvim.appimage"
    echo "[update-nvim] target version  ${target}"
    echo "[update-nvim] current version ${previous}"
    echo "[update-nvim] downloading file ${url}"
    curl  --output ${tmp_bin} --silent -L ${url}
    file_type=$(file ${tmp_bin})
    if [[ $file_type =~ .*executable.* ]]; then
        mv ${tmp_bin} ~/.local/bin/nvim
        chmod +x ~/.local/bin/nvim
        current=$(nvim --version|grep '^NVIM')
        echo "[update-nvim] installed version ${current}"
    else
        echo "[update-nvim] Invalid file ${file_type}; exiting"
        return 1
    fi
}