Assets are not copied

[MaximBalaganskiy]

Stencil version:

`-- @stencil/webpack@0.0.6

I'm submitting a ...
[x] bug report
[ ] feature request

Current behavior:
Assets are not copied to the build folder

Expected behavior:
Assets are copied to the build folder

Steps to reproduce:
Install any stencils components, e.g. npm i simple-buttons. Run webpack.

Other information:
The issue is that the plugin tries to get the assets folder name using the import root which is index.js.
One possible fix is to rename package.json parameters to point to the core file, but this creates other issues:

• stencil build starts giving warnings
• it is impossible to export any additional classes as suggested here