Fix GCC build error by correctly including <utility> header

This is needed to not rely on implementation defined behavior
regarding transitive header includes, here for std::integer_sequence.

include/helpers.hpp

@@ -3,6 +3,7 @@
 #include <fstream>
 #include <iostream>
 #include <iterator>
+#include <utility>
 #include <vector>
 #include "termcolor.hpp"