Browser version needs improvement

[silverwind]

favicon.ico is unreliable on modern sites that use SVG or PNG favicons, which could also be inlined as a datauri. I think we need to get creative and find better methods. Maybe a <script> tag could be of use because it's inherently cross-origin compatible.

[sindresorhus]

It's only unreliable when you don't know the site it's going to be used one. Favicon serves the purpose of is-online fine as we have a hardcoded list of hosts, but since this module accepts user specified hosts, I guess this makes sense. Or we could just document that the hosts needs to have a /favicon.ico.

[detj]

@sindresorhus should also document that the timeout option will not work in browsers. #50

[detj]

@sindresorhus should also document that the timeout option will not work in browsers. #50

landed in 4dd216c