Bump gson from 2.5 to 2.8.9 in /java/HRWebApp (#204)

Bumps [gson](https://github.com/google/gson) from 2.5 to 2.8.9.
- [Release notes](https://github.com/google/gson/releases)
- [Changelog](https://github.com/google/gson/blob/master/CHANGELOG.md)
- [Commits](google/gson@gson-parent-2.5...gson-parent-2.8.9)

---
updated-dependencies:
- dependency-name: com.google.code.gson:gson
  dependency-type: direct:production
...

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Author: dependabot[bot]

java/HRWebApp/pom.xml

@@ -19,7 +19,7 @@
     <dependency>
       <groupId>com.google.code.gson</groupId>
       <artifactId>gson</artifactId>
-      <version>2.5</version>
+      <version>2.8.9</version>
     </dependency>