don't save header in energy.dat

lib/nBodySim.cpp

@@ -68,7 +68,6 @@ void nBodySim::runSimulation(double dt, unsigned nSteps) {
     std::ofstream energyFile("../out/energy.dat");
 
     positionsFile << nParticles_ << " " << skip << " " << dt << std::endl;
-    energyFile << nParticles_ << " " << skip << " " << dt << std::endl;
 
     for (unsigned i=0; i < nSteps; ++i) {