update docs, writeString()
diff --git a/src/jsontestrunner/main.cpp b/src/jsontestrunner/main.cpp
index dba943b..1ec1fb6 100644
--- a/src/jsontestrunner/main.cpp
+++ b/src/jsontestrunner/main.cpp
@@ -185,7 +185,7 @@
     Json::Value const& root)
 {
   Json::StreamWriterBuilder builder;
-  return writeString(root, builder);
+  return Json::writeString(builder, root);
 }
 static int rewriteValueTree(
     const std::string& rewritePath,