Use pre-increment also for native types

Now that we use pre-increment on enums, it
make sense, for code style uniformity, to
swith to pre-increment also for native types,
although there is no speed difference.

No functional change.

src/main.cpp

@@ -43,7 +43,7 @@ int main(int argc, char* argv[]) {
 
   std::string args;
 
-  for (int i = 1; i < argc; i++)
+  for (int i = 1; i < argc; ++i)
       args += std::string(argv[i]) + " ";
 
   UCI::loop(args);