Revert "chore(package): update webpack-dev-middleware to version 1.8.1"
Revert "chore(package): update webpack-dev-middleware to version 1.8.1"

This reverts commit 888576dbdadc60d243e8927226a5d591a3b92e3c.

This downgrades to 1.6.1 because the upgrade was causing a bundle 404 somehow.

aviarypl/mozilla-l10n-addons-frontend,aviarypl/mozilla-l10n-addons-frontend,squarewave/addons-frontend,kumar303/addons-frontend,jasonthomas/addons-frontend,tsl143/addons-frontend,mstriemer/addons-frontend,muffinresearch/addons-frontend,mozilla/addons-frontend,squarewave/addons-frontend,muffinresearch/addons-frontend,mozilla/addons-frontend,tsl143/addons-frontend,mozilla/addons-frontend,tsl143/addons-frontend,squarewave/addons-frontend,kumar303/addons-frontend,tsl143/addons-frontend,mozilla/addons-frontend,aviarypl/mozilla-l10n-addons-frontend,aviarypl/mozilla-l10n-addons-frontend,kumar303/addons-frontend,kumar303/addons-frontend,muffinresearch/addons-frontend,mstriemer/addons-frontend,jasonthomas/addons-frontend,mstriemer/addons-frontend,jasonthomas/addons-frontend