[libnblog] Use new jsoncpp API

Reader / StyledWriter are deprecated upstream

Bug: 170642246
Change-Id: Id48592c7ef47392910b771e0da4d1d306b3424d8
diff --git a/media/libnblog/ReportPerformance.cpp b/media/libnblog/ReportPerformance.cpp
index aa678ba..4c78b01 100644
--- a/media/libnblog/ReportPerformance.cpp
+++ b/media/libnblog/ReportPerformance.cpp
@@ -92,8 +92,8 @@
         (*dataJson)["threadNum"] = item.first;
         root.append(*dataJson);
     }
-    Json::StyledWriter writer;
-    std::string rootStr = writer.write(root);
+    Json::StreamWriterBuilder factory;
+    std::string rootStr = Json::writeString(factory, root);
     write(fd, rootStr.c_str(), rootStr.size());
 }