fix(rich-text-types): resolve generated JSON schemas

[z0al]

Using the new validateRichTextDocument fails due to require('./generated/{nodeType}.json') unable to resolve the file.

Before:

dist/
  lib/
    schemas/
      generated/
      index.js // importing the helper directly works
  rich-text-types.es5.js // a single bundle of the whole source code. It fails to locate ./generated

After:

dist/
  schemas/
    generated/
    index.js // importing the helper directly still works
  index.js // now calls schemas/generated/index.js since the code no longer bundled together.