refactor: fix lint warning on public/js/index.js
refactor: fix lint warning on public/js/index.js

Signed-off-by: BoHong Li <9f7d63b58e4573d72eb50da9dd011b77faf5d27f@gmail.com>

hackmdio/hackmd,hackmdio/hackmd,hackmdio/hackmd,jackycute/HackMD,jackycute/HackMD,jackycute/HackMD