json: format output with 4-space indentation

Use `dump(4)` instead of `dump()` to generate JSON with
4-space indentation, improving readability of written files.

Change-Id: Ib0a0e932bba76091dbb6a6b89640e579df289747
Signed-off-by: George Liu <liuxiwei@ieisystem.com>
diff --git a/oem/nvidia/biosconfigcommands.cpp b/oem/nvidia/biosconfigcommands.cpp
index 6952d85..cce5b0c 100644
--- a/oem/nvidia/biosconfigcommands.cpp
+++ b/oem/nvidia/biosconfigcommands.cpp
@@ -92,7 +92,7 @@
     try
     {
         std::ofstream ofs(biosPasswordFilePath, std::ios::out);
-        const auto& writeData = json.dump();
+        const auto& writeData = json.dump(4);
         ofs << writeData;
         ofs.close();
     }