Support for version 3

[nunof07]

Hi @Mistereo ,

Thank you for this package!

Do you plan on supporting version 3 of Linaria (currently in beta)?
It splits Linaria into different packages (@linaria/webpack-loader, etc.).

From the Linaria docs the installation process seems the same, except the different naming, so in next-linaria I tried replacing this:

            loader: require.resolve('linaria/loader'),

With this:

            loader: '@linaria/webpack-loader',

But got some weird errors.

Anyway, I still got it to work with the previous version. Thanks.