chore(package): update babel-preset-stage-2 to version 6.18.0
chore(package): update babel-preset-stage-2 to version 6.18.0

https://greenkeeper.io/
jasonthomas/addons-frontend,aviarypl/mozilla-l10n-addons-frontend,aviarypl/mozilla-l10n-addons-frontend,kumar303/addons-frontend,mozilla/addons-frontend,squarewave/addons-frontend,tsl143/addons-frontend,kumar303/addons-frontend,mozilla/addons-frontend,jasonthomas/addons-frontend,mozilla/addons-frontend,jasonthomas/addons-frontend,kumar303/addons-frontend,squarewave/addons-frontend,tsl143/addons-frontend,tsl143/addons-frontend,aviarypl/mozilla-l10n-addons-frontend,tsl143/addons-frontend,aviarypl/mozilla-l10n-addons-frontend,squarewave/addons-frontend,mozilla/addons-frontend,kumar303/addons-frontend