DataFrame and Series append deprecated

Created by: peraaslid

FutureWarning: The series.append method is deprecated and will be removed from pandas in a future version. Use pandas.concat instead. df = df.append(new_row)

https://github.com/sintef-energy/pyshop/blob/0c80f9e6d434949beb371f14eec46b014f1fcff8/pyshop/shopcore/shop_api.py#L245