update description of browser.shell.shortcutFavicons
update description of browser.shell.shortcutFavicons

https://github.com/pyllyukko/user.js/pull/279#issuecomment-301300772
Toromtomtom/user.js,pyllyukko/user.js,pyllyukko/user.js,nodiscc/user.js,Toromtomtom/user.js,nodiscc/user.js