Sync with underscore-java.

Author: javadev

src/main/java/com/github/underscore/lodash/U.java

@@ -2296,7 +2296,7 @@ public static Builder fromXml(final String xml) {
         }
 
         public String toJson() {
-            return Xml.toXml(data);
+            return Json.toJson(data);
         }
 
         public static Builder fromJson(final String json) {