Run Clang-tidy with modernize-use-auto (#1077)

* Run clang-tidy modify with modernize-use-auto
* Use using instead of typedef
diff --git a/example/readFromString/readFromString.cpp b/example/readFromString/readFromString.cpp
index ce32236..c27bbd5 100644
--- a/example/readFromString/readFromString.cpp
+++ b/example/readFromString/readFromString.cpp
@@ -11,7 +11,7 @@
  */
 int main() {
   const std::string rawJson = R"({"Age": 20, "Name": "colin"})";
-  const int rawJsonLength = static_cast<int>(rawJson.length());
+  const auto rawJsonLength = static_cast<int>(rawJson.length());
   constexpr bool shouldUseOldWay = false;
   JSONCPP_STRING err;
   Json::Value root;