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

* Run clang-tidy modify with modernize-use-auto
* Use using instead of typedef
diff --git a/src/jsontestrunner/main.cpp b/src/jsontestrunner/main.cpp
index dbfbe98..f6b1a4d 100644
--- a/src/jsontestrunner/main.cpp
+++ b/src/jsontestrunner/main.cpp
@@ -58,7 +58,7 @@
     return "";
   fseek(file, 0, SEEK_END);
   long const size = ftell(file);
-  size_t const usize = static_cast<unsigned long>(size);
+  const auto usize = static_cast<size_t>(size);
   fseek(file, 0, SEEK_SET);
   char* buffer = new char[size + 1];
   buffer[size] = 0;