Bump gson from 2.2.4 to 2.8.9

Bumps [gson](https://github.com/google/gson) from 2.2.4 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-2.2.4...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>

Author: dependabot[bot]

pom.xml

@@ -30,7 +30,7 @@
         <cdap.version>6.8.0</cdap.version>
         <hadoop.version>2.10.2</hadoop.version>
         <hydrator.version>2.10.0</hydrator.version>
-        <gson.version>2.2.4</gson.version>
+        <gson.version>2.8.9</gson.version>
         <common.logging.version>1.2</common.logging.version>
         <junit.version>4.11</junit.version>
         <mockito.version>1.10.19</mockito.version>