chore(package): update sass-loader to version 5.0.1
chore(package): update sass-loader to version 5.0.1

Closes #1718

https://greenkeeper.io/

tsl143/addons-frontend,kumar303/addons-frontend,aviarypl/mozilla-l10n-addons-frontend,aviarypl/mozilla-l10n-addons-frontend,tsl143/addons-frontend,aviarypl/mozilla-l10n-addons-frontend,kumar303/addons-frontend,tsl143/addons-frontend,kumar303/addons-frontend,mozilla/addons-frontend,kumar303/addons-frontend,tsl143/addons-frontend,mozilla/addons-frontend,mozilla/addons-frontend,aviarypl/mozilla-l10n-addons-frontend,mozilla/addons-frontend