old_contents: from rockstar import RockStar
  
  bf_code = "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."
  rock_it_bro = RockStar(days=400, file_name='helloWorld.b', code=bf_code)
  rock_it_bro.make_me_a_rockstar()
  
new_contents: from rockstar import RockStar
  
  bf_code = "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."
  rock_it_bro = RockStar(days=400, file_name='helloWorld.bf', code=bf_code)
  rock_it_bro.make_me_a_rockstar()
  
subject: Change file extension