Bump proguard-maven-plugin from 2.4.0 to 2.5.1 (#1980)

Bumps [proguard-maven-plugin](https://github.com/wvengen/proguard-maven-plugin) from 2.4.0 to 2.5.1.
- [Release notes](https://github.com/wvengen/proguard-maven-plugin/releases)
- [Changelog](https://github.com/wvengen/proguard-maven-plugin/blob/master/CHANGELOG.md)
- [Commits](https://github.com/wvengen/proguard-maven-plugin/commits)

---
updated-dependencies:
- dependency-name: com.github.wvengen:proguard-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

gson/pom.xml

@@ -109,7 +109,7 @@
       <plugin>
         <groupId>com.github.wvengen</groupId>
         <artifactId>proguard-maven-plugin</artifactId>
-        <version>2.4.0</version>
+        <version>2.5.1</version>
         <executions>
           <execution>
             <phase>process-test-classes</phase>