Fix incorrect package for JsonGen annotation

Author: vietj

src/main/java/io/vertx/ext/stomp/Frame.java

@@ -18,7 +18,7 @@
 
 import io.vertx.codegen.annotations.DataObject;
 import io.vertx.codegen.annotations.GenIgnore;
-import io.vertx.codegen.annotations.JsonGen;
+import io.vertx.codegen.json.annotations.JsonGen;
 import io.vertx.core.buffer.Buffer;
 import io.vertx.core.json.JsonObject;
 import io.vertx.ext.stomp.impl.FrameException;

src/main/java/io/vertx/ext/stomp/StompClientOptions.java

@@ -17,7 +17,7 @@
 package io.vertx.ext.stomp;
 
 import io.vertx.codegen.annotations.DataObject;
-import io.vertx.codegen.annotations.JsonGen;
+import io.vertx.codegen.json.annotations.JsonGen;
 import io.vertx.core.json.JsonObject;
 import io.vertx.core.net.NetClientOptions;
 

src/main/java/io/vertx/ext/stomp/StompServerOptions.java

@@ -17,7 +17,7 @@
 package io.vertx.ext.stomp;
 
 import io.vertx.codegen.annotations.DataObject;
-import io.vertx.codegen.annotations.JsonGen;
+import io.vertx.codegen.json.annotations.JsonGen;
 import io.vertx.core.Handler;
 import io.vertx.core.json.JsonObject;
 import io.vertx.core.net.NetServerOptions;