fix stock creation

create_new_stock.py

@@ -2,5 +2,5 @@ import model
 from admin_console import cleanup
 
 if __name__ == '__main__':
-    print(model.new_stock(input('How long will the initial selling be available? (minutes):')))
+    print(model.new_stock(float(input('How long will the initial selling be available? (minutes):'))))
     cleanup()