fix(semantic-ui): update main field

[bluwy]

Reasons for making this change

The main points to dist/cjs/index.js which doesn't exist. It should be dist/index.js

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests. I've run npm run test:update to update snapshots, if needed.
  • I've updated docs if needed
  • I've updated the changelog with a description of the PR
• I'm adding a new feature
  • I've updated the playground with an example use of the feature

[heath-freenome]

@bluwy Good catch, would you be willing to rebase this change onto the rjsf-v5 branch as that branch will soon be merged to the master?

[bluwy]

Done!