Fix: Upgrade markdown-to-jsx

Closes styleguidist#1181

Changelog: 🚀

## Breaking changes

### Drop webpack 3 support

Webpack 3 is no longer supported, webpack 4 is the minimum required version.

As a side effect you shouldn’t see any webpack warnings when you run Styleguidist.

We’ve also replaced no longer maintainer uglify-es with Terser to minify production JavaScript bundle.

* styleguidist#1175, styleguidist#1178 by @derz
* styleguidist#1165 by @elevatebart
* styleguidist#1148 by @elevatebart
* styleguidist#915, styleguidist#1023 by @stepancar
* styleguidist#1180 by @AndreyGladkov

Fix: Lock Buble version to use the same Acorn version that is used in…

… Styleguidist

Fix: Allow assetsDir to be an array (styleguidist#1167)

Fix: Do not render an empty props table for TypeScript projects (styl…

…eguidist#1158)

Fix: Regression: component patterns return nothing on Windows (styleg…

…uidist#1133)

Fix: Add inline-scroll on props table (styleguidist#1131)

Fix: Fix duplicated components with default glob on windows (stylegui…

…dist#1128)

Closes styleguidist#1127

Fix: Allow pathline to wrap (styleguidist#1125)

The "Pathline" breaks the responsive view if it gets too long as there will be a horizontal scrollbar

Fix: Add custom focus outline for <summary> element