chore(package): update webpack-hot-middleware to version 2.18.0 (#2217)
chore(package): update webpack-hot-middleware to version 2.18.0 (#2217)

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