Bump japicmp-maven-plugin from 0.15.4 to 0.15.6 (#93)

Bump japicmp-maven-plugin from 0.15.4 to 0.15.6 (#93)

Bumps [japicmp-maven-plugin](https://github.com/siom79/japicmp) from 0.15.4 to 0.15.6.
- [Release notes](https://github.com/siom79/japicmp/releases)
- [Changelog](https://github.com/siom79/japicmp/blob/master/release.py)
- [Commits](https://github.com/siom79/japicmp/compare/japicmp-base-0.15.4...japicmp-base-0.15.6)

---
updated-dependencies:
- dependency-name: com.github.siom79.japicmp:japicmp-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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