Update shrpx_config.cc

declaration of make_socket_closeonexec need the proper scope here, it was there per request at https://github.com/tatsuhiro-t/nghttp2/pull/142 , not sure why is was removed.

src/shrpx_config.cc

@@ -253,7 +253,7 @@ FILE *open_file_for_write(const char *filename) {
 
   // We get race condition if execve is called at the same time.
   if (fd != -1) {
-    make_socket_closeonexec(fd);
+    util::make_socket_closeonexec(fd);
   }
 #endif
   if (fd == -1) {