Bump org.codehaus.mojo:flatten-maven-plugin in /ladybug-frontend-servlet (#891)

Bumps [org.codehaus.mojo:flatten-maven-plugin](https://github.com/mojohaus/flatten-maven-plugin) from 1.7.3 to 1.8.0.
- [Release notes](https://github.com/mojohaus/flatten-maven-plugin/releases)
- [Commits](mojohaus/flatten-maven-plugin@1.7.3...1.8.0)

---
updated-dependencies:
- dependency-name: org.codehaus.mojo:flatten-maven-plugin
  dependency-version: 1.8.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]