Prettier introduced

• dependencies kept up to date
• Improve tests with shorter expire policy + no gzip #777
• Add support for viewport option #784 (thanks @gmetais)
• Adjustments to lazyloadable images #787 (thanks @gmetais)
• waitFor is now deprecated #788
• Update Dockerfile, Use node:14-stretch-slim base image #789
• Tests: use the latest macbre/nginx-brotli - 1.19.3 #786

npm version 2.0.0-alpha3 
npm publish --tag next