Relative, rather than absolute, baseUrl

When accessing https://gaearon.github.io/react-hot-loader/ (notice https) in Chrome the .css files are being blocked due to https -> http request.

Message received:
'[blocked] The page at 'https://gaearon.github.io/react-hot-loader/' was loaded over HTTPS, but ran insecure content from 'http://gaearon.github.io/react-hot-loader/public/css/syntax.css': this content should also be loaded over HTTPS.'