Fix incorrect main script path in package.json and set package to type: module

[khromov]

The path to module and main is not correct. Without this change you get the following Rollup error when building (note the import is in a .ts file, not .svelte)

(!) Plugin typescript: @rollup/plugin-typescript TS2307: Cannot find module '@crownframework/svelte-error-boundary' or its corresponding type declarations.
src/lib/error.ts: (1:32)