Support HEAD request

[sindresorhus]

See #924 (comment)

[alexander-akait]

We already support difference methods (https://github.com/webpack/webpack-dev-middleware#methods), by defaults we supports only GET. What is problem? Support by default all possible? Or support only HEAD? Or no documentation about this?

[sindresorhus]

What's the purpose of limiting it?

[alexander-akait]

@sindresorhus historical reason, previously we support only GET request for webpack-dev-middleware so we support only GET for webpack-dev-server, now we support all possible requests for webpack-dev-middleware, but by default we still support only GET. We can change this, because i can't see any problems to allowing any requests. Anyway can you provide case, just for information and future improvements, thanks.

[sindresorhus]

I use HEAD request to check whether the server is running.

Another use-case here: #924 (comment)

[alexander-akait]

Thanks, mark as feature, feel free to send a PR if you want this asap