deps: bump com.google.cloud.tools:appengine-maven-plugin (#2226)

Bumps [com.google.cloud.tools:appengine-maven-plugin](https://github.com/GoogleCloudPlatform/app-maven-plugin) from 2.4.4 to 2.5.0.
- [Release notes](https://github.com/GoogleCloudPlatform/app-maven-plugin/releases)
- [Changelog](https://github.com/GoogleCloudPlatform/app-maven-plugin/blob/master/CHANGELOG.md)
- [Commits](GoogleCloudPlatform/app-maven-plugin@v2.4.4...v2.5.0)

---
updated-dependencies:
- dependency-name: com.google.cloud.tools:appengine-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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