'DataFrame' object has no attribute 'ix'

[williamjin1992]

Hi, I'm a beginner of time series econometrics. As I installed pyflux on my computer, when I running the code in https://pyflux.readthedocs.io/en/latest/arima.html and it report an error of ''DataFrame' object has no attribute 'ix'', I guess the developer may not update their source code for a while and the .ix attribute for DataFrame is deprecated, so I politly suggest that this should be modified to accomendate the latest version of pandas.