Dependency major version updates

[fhennig]

There are a lot of major version bumps which require new node versions, breaking changes etc.
This needs to be tackled manually.

Package Current Wanted Latest Location Depended by
cssnano 4.1.11 4.1.11 5.1.14 node_modules/cssnano documentation-ui
eslint 6.8.0 6.8.0 8.31.0 node_modules/eslint documentation-ui
eslint-config-standard 14.1.1 14.1.1 17.0.0 node_modules/eslint-config-standard documentation-ui
eslint-plugin-promise 4.3.1 4.3.1 6.1.1 node_modules/eslint-plugin-promise documentation-ui
eslint-plugin-standard 4.1.0 4.1.0 5.0.0 node_modules/eslint-plugin-standard documentation-ui
fancy-log 1.3.3 1.3.3 2.0.0 node_modules/fancy-log documentation-ui
fs-extra 9.1.0 9.1.0 11.1.0 node_modules/fs-extra documentation-ui
gulp-imagemin 7.1.0 7.1.0 8.0.0 node_modules/gulp-imagemin documentation-ui
highlight.js 10.7.3 10.7.3 11.7.0 node_modules/highlight.js documentation-ui
postcss-custom-properties 11.0.0 11.0.0 12.1.11 node_modules/postcss-custom-properties documentation-ui
postcss-import 14.1.0 14.1.0 15.1.0 node_modules/postcss-import documentation-ui
prettier-eslint 12.0.0 12.0.0 15.0.1 node_modules/prettier-eslint documentation-ui
stylelint 13.13.1 13.13.1 14.16.1 node_modules/stylelint documentation-ui
stylelint-config-standard 22.0.0 22.0.0 29.0.0 node_modules/stylelint-config-standard documentation-ui

Edit: Since the project is built with gulp, it looks like you need to uprade the gulp dependencies. Some of them don't seem to receive updates anymore. It's all a bit messy. For example eslint is used by gulp-eslint, but the package is abandoned. In general, Gulp seems to have lost a lot of steam.

Dependency Dashboard:
#130

[fhennig]

It would be good to investigate more how to build process actually works #30