Added GameController to use toJson().

pom.xml

@@ -54,6 +54,11 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-test</artifactId>
 			<scope>test</scope>
+		</dependency>
+    <dependency>
+  <groupId>com.google.code.gson</groupId>
+  <artifactId>gson</artifactId>
+  <version>2.8.6</version>
 </dependency>
 		<dependency>
 			<groupId>org.apache.tomcat.embed</groupId>