fix class reference issue

Author: paulvangentcom

simulation.py

@@ -162,7 +162,7 @@ def run(self):
 
 whilei<self.Config.simulation_steps:
 try:
-sim.tstep()
+self.tstep()
 exceptKeyboardInterrupt:
 print('\nCTRL-C caught, exiting')
 sys.exit(1)