fix typo

navipy/moving/agent.py

@@ -435,7 +435,7 @@ the agent motion, or
                 print('Remain {}, done in {}'.format(remain, remain*t_peritem))
                 if filename is not None:
                     self.velocities.to_hdf(filename, key='velocities')
-
+                prev_nline = nline
             nline += 1
         return self.velocities.copy()