Bypass client initialisation in a DOM-less environment.

[richardgoater]

Hello, really appreciate this project, thank you. I've added a few conditionals preventing the middleware from breaking the build when the DOM isn't present, in my case when using static-site-generator-webpack-plugin. I've also removed some duplicate keys from the .eslint file, which gave me a few errors in Atom. Let me know if you'd like me to change anything,

[glenjamin]

I've just merged this with some slight tweaks and some unit tests.

I also moved the document check, let me know if this causes issues.

Released as 2.6.1

[richardgoater]

Thanks for taking the time to look at this @glenjamin. I'm afraid the new document check does indeed cause issues for me, I think document is still accessed without a check on this line: https://github.com/glenjamin/webpack-hot-middleware/blob/master/client-overlay.js#L3.

[glenjamin]

Whoops, that was sloppy 2.6.2 released

[richardgoater]

Not a problem sir, thanks very much for sorting it 👍