Used std::put_time instead of std::strftime in SystemInfo

#include <set>

#include <iomanip>

#include <cstring>

#include <ctime>

#include <unistd.h>

#include <sys/utsname.h>

{

   const std::time_t time_since_epoch = std::time( nullptr );

   std::tm* localtime = std::localtime( &time_since_epoch );

   // TODO: use std::put_time in the future (available since GCC 5)

//   std::stringstream ss;

//   ss << std::put_time( localtime, format );

//   return String( ss.str().c_str() );

   char buffer[1024];

   std::strftime( buffer, 1024, format, localtime );

   return String( buffer );

   std::stringstream ss;

   ss << std::put_time( localtime, format );

   return String( ss.str().c_str() );

}