Fix: remove webpack 4 deprecation warning

[elevatebart]

After seeing the following warning a great enough number of times, I decided to tackle the issue.

(node:13435) DeprecationWarning: Tapable.plugin is deprecated. Use new API on `.hooks` instead

Three object were still using the webpack 3 way:

• StyleguidistOptionsPlugin, but I guess you already worked on that
• bin/styleguidist.js that was hooking directly onto webpack
• [email protected] that is incompatible with webpack 4.

I therefore upgraded the latest and fixed both the other files. The warning is gone.

Enjoy

[codecov-io]

Codecov Report

Merging #1148 into master will increase coverage by <.01%.
The diff coverage is 100%.

Impacted Files	Coverage Δ
scripts/utils/StyleguidistOptionsPlugin.js	100% <100%> (ø)	⬆️

[sapegin]

Cool! This is very nice! Couple of minor comments.

[elevatebart]

Hello @sapegin I finally found the time to run those webpack 3 tests. Even if the tests seem to pass, when testing manually I have a big old error in webpack-dev-server...

Cannot destructure property `compile` of 'undefined' or 'null'.

the faulty line obviously being:

const { compile, invalid, done } = compiler.hooks;

I wonder if I could load multiple versions of the dev server and call them depending on the version of webpack.

I will recreate this PR on the next branch in order to probably drop webpack 3 support in 8.

[elevatebart]

I removed the update of webpack-dev-server and left the other fixes.
This is a first step towards compatibility, since we should not drop webpack 3 in the middle of a minor version.

Tested with webpack 3 & webpack 4.
Webpack3, purrs like a kitten.
Webpack4, still has the warning but works.

[sapegin]

I believe this was either merged manually of fixed by another pull request. Thanks for the contribution!