Bump gson from 2.8.6 to 2.8.9 in /core

Bumps [gson](https://github.com/google/gson) from 2.8.6 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-2.8.6...gson-parent-2.8.9)

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

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

core/pom.xml

@@ -19,7 +19,7 @@
         <brave-opentracing.version>0.31.1</brave-opentracing.version>
         <zipkin-reporter.version>2.7.4</zipkin-reporter.version>
         <ch.qos.logback.version>1.2.3</ch.qos.logback.version>
-        <gson.version>2.8.6</gson.version>
+        <gson.version>2.8.9</gson.version>
     </properties>
 
     <dependencies>