Update cleanHostValue so it never returns invalid hostname characters

[myndzi]

No description provided.

[myndzi]

This should fix the remaining case for #54.

URL.parse strangely allows + in hostnames, but as far as I can tell, they're not acceptable for regular hostnames (as used in DNS and the web at large), and they are special in regex, so I've excluded them. cleanHostValue will now only return strings that contain entirely valid hostname characters, or the empty string. This fixes the above case, passes all the tests, and seems sane; it still uses url.parse for parsing, so there is a possible edge case where a hostname including '+' will get successfully parsed by url.parse but will be returned as invalid/empty from cleanHostValue.

[thom4parisot]

Quite subtle, thanks :-)