whitespace cleanup

src/SPIN/atom_vec_spin.cpp

src/SPIN/atom_vec_spin.h

src/SPIN/compute_spin.cpp

src/SPIN/fix_langevin_spin.cpp

src/SPIN/fix_langevin_spin.h

src/SPIN/fix_nve_spin.cpp

src/SPIN/fix_nve_spin.h

src/SPIN/fix_precession_spin.cpp

src/SPIN/fix_precession_spin.h

src/SPIN/pair_spin.cpp

src/SPIN/pair_spin.h

src/SPIN/pair_spin_dmi.cpp

src/SPIN/pair_spin_dmi.h

src/SPIN/pair_spin_exchange.cpp

src/SPIN/pair_spin_exchange.h

src/SPIN/pair_spin_magelec.cpp

src/SPIN/pair_spin_magelec.h

src/SPIN/pair_spin_neel.cpp

src/SPIN/pair_spin_neel.h

src/atom.cpp