[fuelcell] update reference solution
Commit fb5b0cc1 of dumux fixed the enthalpy calculation of the 2pnc model. This slightly affects the solution of the fuelcell example. Update the corresponding reference solution.
Commit fb5b0cc1 of dumux fixed the enthalpy calculation of the 2pnc model. This slightly affects the solution of the fuelcell example. Update the corresponding reference solution.