feat: support HEAD method by default

[alexander-akait]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Support HEAD method by default

Breaking Changes

No

Additional Info

No

[alexander-akait]

/cc @hiroppy need review

[codecov]

Codecov Report

Merging #398 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #398   +/-   ##
=======================================
  Coverage   97.03%   97.03%           
=======================================
  Files           7        7           
  Lines         304      304           
  Branches      103      103           
=======================================
  Hits          295      295           
  Misses          9        9

Impacted Files	Coverage Δ
lib/middleware.js	94.91% <100%> (ø)	⬆️

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[hiroppy]

🤔

https://dev.azure.com/webpack/webpack-dev-middleware/_build/results?buildId=2689

> webpack-dev-middleware@3.6.2 security /home/vsts/work/1/s
> npm audit

npm ERR! code ENOAUDIT
npm ERR! audit Your configured registry (https://registry.npmjs.org/) does not support audit requests, or the audit endpoint is temporarily unavailable.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/vsts/.npm/_logs/2019-05-14T19_07_11_131Z-debug.log
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! webpack-dev-middleware@3.6.2 security: `npm audit`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the webpack-dev-middleware@3.6.2 security script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /home/vsts/.npm/_logs/2019-05-14T19_07_14_437Z-debug.log
##[error]Bash exited with code '1'.
##[section]Finishing: Run NPM audit

[alexander-akait]

npm register is very bad

[hiroppy]

Thanks!