themeable() merging issues

[Aurimas]

In the nested theme case shown below:

const themeA = {};
const themeB = {
    nested: {
        bar: 'bar'
    }
};
themeable(themeA, themeB);

we get an error:
Uncaught Error: You are merging a string "" with an Object,Make sure you are passing the proper theme descriptors.

[Kirill Agalakov]

@powah I believe I fixed it under #47 but it wasn't released, only merged. Try to checkout current master.

[Kirill Agalakov]

@javivelasco Could you please release current master as 2.1.0?

[Javi Velasco]

Releasing today!