build(deps): bump petgraph from 0.6.2 to 0.6.3

Bumps [petgraph](https://github.com/petgraph/petgraph) from 0.6.2 to 0.6.3.
- [Release notes](https://github.com/petgraph/petgraph/releases)
- [Changelog](https://github.com/petgraph/petgraph/blob/master/RELEASES.rst)
- [Commits](https://github.com/petgraph/petgraph/commits/0.6.3)

---
updated-dependencies:
- dependency-name: petgraph
  dependency-type: indirect
  update-type: version-update:semver-patch
...

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