build(deps): bump bn.js from 5.1.3 to 5.2.0 in /token-swap/js

Bumps [bn.js](https://github.com/indutny/bn.js) from 5.1.3 to 5.2.0.
- [Release notes](https://github.com/indutny/bn.js/releases)
- [Changelog](https://github.com/indutny/bn.js/blob/master/CHANGELOG.md)
- [Commits](indutny/bn.js@v5.1.3...v5.2.0)

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