fix(stats): add errors-warnings preset

[niedzielski]

Add the new errors-warnings preset shipped in v4.31.0. Keeping
webpack-dev-server presets supported consistent with Webpack will make
both tools easier to use.

https://github.com/webpack/webpack/releases/tag/v4.31.0

https://github.com/webpack/webpack/pull/8919/files#diff-baf371f5446dc9bc4b41022587e05b48

• This is a bugfix
• This is a feature
• This is a code refactor
• This is a test update
• This is a docs update
• This is a metadata update

For Bugs and Features; did you add new tests?

Motivation / Use-Case

Breaking Changes

Additional Info

[codecov]

Codecov Report

Merging #1895 into master will decrease coverage by 3.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1895      +/-   ##
==========================================
- Coverage    91.2%   88.03%   -3.18%     
==========================================
  Files          14       14              
  Lines         819      819              
  Branches      260      260              
==========================================
- Hits          747      721      -26     
- Misses         68       84      +16     
- Partials        4       14      +10

Impacted Files	Coverage Δ
lib/Server.js	85.96% <0%> (-5.62%)	⬇️

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[hiroppy]

Thanks!