Bump gson from 2.8.2 to 2.8.9

Bumps [gson](https://github.com/google/gson) from 2.8.2 to 2.8.9.
- [Release notes](https://github.com/google/gson/releases)
- [Changelog](https://github.com/google/gson/blob/master/CHANGELOG.md)
- [Commits](https://github.com/google/gson/compare/gson-parent-2.8.2...gson-parent-2.8.9)

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

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/pom.xml b/pom.xml
index 715e0c2..edcf760 100644
--- a/pom.xml
+++ b/pom.xml
@@ -11,7 +11,7 @@
         <source.level>1.8</source.level>
         <target.level>1.8</target.level>
         <dubbo.version>2.7.0-SNAPSHOT</dubbo.version>
-        <gson.version>2.8.2</gson.version>
+        <gson.version>2.8.9</gson.version>
         <junit.version>4.12</junit.version>
         <hamcrest.version>1.3</hamcrest.version>
         <mockito.version>2.18.3</mockito.version>