Add bugs metadata to package.json

[MercyMo]

The published npm package react-barcode@1.6.1 exposes repository, homepage, and license metadata, but npm view react-barcode@1.6.1 bugs --json returns no value.

Adding standard npm bugs metadata would let npm and downstream tooling point users directly to this repository's issue tracker:

"bugs": {
  "url": "https://github.com/kciter/react-barcode/issues"
}

I also checked the current master branch package.json and it appears to be missing the same field, so this should be a small manifest-only cleanup.