DataFrame has no append (deprecated) for oanda currencies

[mathisloevenich]

In the get.py there are DataFrames concatenated via append which is deprecated I guess:

here is my solution (workaround):

 if provider == 'oanda':
        csv_files = glob.glob('{0}/currencies/oanda/{1}/{2}/*.csv'.format(data_dir, instrument, year))
        data_frames = [pd.read_csv(csv_file, index_col=0) for csv_file in csv_files]
        price_data = pd.concat(data_frames)