Bump github.com/prometheus/client_model from 0.2.0 to 0.3.0

Bumps [github.com/prometheus/client_model](https://github.com/prometheus/client_model) from 0.2.0 to 0.3.0.
- [Release notes](https://github.com/prometheus/client_model/releases)
- [Commits](https://github.com/prometheus/client_model/compare/v0.2.0...v0.3.0

)

---
updated-dependencies:
- dependency-name: github.com/prometheus/client_model
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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