--history_to_use doesn't work with integer values

[dw-sun]

When i use the integer(for example 100) as value for for --history_to_use, error happens.

File "C:\Users\hello\Repo\eiten\argchecker.py", line 8, in __init__
    self.check_arguments(args)
  File "C:\Users\hello\Repo\eiten\argchecker.py", line 20, in check_arguments
    assert not(args.history_to_use != "all" and int(args.history_to_use_int) <
AttributeError: 'Namespace' object has no attribute 'history_to_use_int'

args.history_to_use_int should be the reason, there isn't history_to_use_int argument parameter

[tradytics]

Shoot, do you wanna take a pass at fixing this and submit a PR? If not, I'll fix it over the weekend and let you know.

This was caused by a new PR recently. My apologies.