Can't use with Jest

[nornagon]

When trying to test a component using svelte-error-boundary under Jest, I get the following error:

    Cannot find module '@crownframework/svelte-error-boundary' from 'src/Thing.svelte'

I think this is because the "main" field in package.json is incorrect. Additionally, the index.js file uses module syntax, which confuses Jest—it expects the module to be compiled, I think.