message: fixing fermionoperator bug with gcc 5
diff: @@ -42,6 +42,11 @@ public:
  std::get<1>(*this) = {};
  }
  + FermionTerm(double c) {
  + std::get<0>(*this) = std::complex<double>(c,0.0);
  + std::get<1>(*this) = {};
  + }
  +
  FermionTerm(std::complex<double> c, Operators ops) {
  std::get<0>(*this) = c;
  std::get<1>(*this) = ops;
  