message: bytes: Use std::pow.
diff: #include <elle/bytes.hh>
  +#include <cmath>
  +
  #include <elle/printf.hh>
  #include <elle/unreachable.hh>
  @@ -21,7 +23,7 @@ namespace elle
  auto scale = si ? 1000. : 1024.;
  auto const& unit = si ? engineer : computer;
  for (uint64_t i = 0; i < size; ++i)
  - if (i == size - 1 || bytes / pow(scale, i+1) < 1)
  + if (i == size - 1 || bytes / std::pow(scale, i+1) < 1)
  return elle::sprintf("%.1f %s", bytes / pow(scale, i), unit[i]);
  elle::unreachable();
  }
  