http service: use http-api gson instance

http-service/src/main/java/net/runelite/http/service/SpringWebMvcConfigurer.java

@@ -25,6 +25,7 @@
 package net.runelite.http.service;
 
 import java.util.List;
+import net.runelite.http.api.RuneLiteAPI;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.http.MediaType;
 import org.springframework.http.converter.HttpMessageConverter;
@@ -53,6 +54,8 @@ public class SpringWebMvcConfigurer extends WebMvcConfigurerAdapter
 	@Override
 	public void configureMessageConverters(List<HttpMessageConverter<?>> converters)
 	{
-		converters.add(new GsonHttpMessageConverter());
+		GsonHttpMessageConverter gsonHttpMessageConverter = new GsonHttpMessageConverter();
+		gsonHttpMessageConverter.setGson(RuneLiteAPI.GSON);
+		converters.add(gsonHttpMessageConverter);
 	}
 }