build(deps): bump bn.js from 5.2.0 to 5.2.1 in /token-swap/js

Bumps [bn.js](https://github.com/indutny/bn.js) from 5.2.0 to 5.2.1.
- [Release notes](https://github.com/indutny/bn.js/releases)
- [Changelog](https://github.com/indutny/bn.js/blob/master/CHANGELOG.md)
- [Commits](indutny/bn.js@v5.2.0...v5.2.1)

---
updated-dependencies:
- dependency-name: bn.js
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>