add line in the end of pair_lj_gromacs.cpp

src/EXTRA-PAIR/pair_lj_gromacs.cpp

@@ -441,4 +441,4 @@ void *PairLJGromacs::extract(const char *str, int &dim)
   if (strcmp(str, "epsilon") == 0) return (void *) epsilon;
   if (strcmp(str, "sigma") == 0) return (void *) sigma;
   return nullptr;
-}
+}