Bump gson from 1.7.2 to 2.8.9 (#7)

Bumps [gson](https://github.com/google/gson) from 1.7.2 to 2.8.9.

pom.xml

@@ -8,7 +8,7 @@ http://maven.apache.org/xsd/maven-4.0.0.xsd">
         <dependency>
             <groupId>com.google.code.gson</groupId>
             <artifactId>gson</artifactId>
-            <version>1.7.2</version>
+            <version>2.8.9</version>
         </dependency>
         <dependency>
             <groupId>com.fasterxml.jackson.core</groupId>