Add gson to dependencies

Author: junichi11

pom.xml

@@ -134,6 +134,11 @@
             <artifactId>swingx-0.9.5</artifactId>
             <version>RELEASE72</version>
         </dependency>
+        <dependency>
+            <groupId>com.google.code.gson</groupId>
+            <artifactId>gson</artifactId>
+            <version>2.3.1</version>
+        </dependency>
     </dependencies>
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>