`StatisticMSAS` raises undesirable `FutureWarning`

[fealho]

Error Description

Running the compute method for StatisticMSAS produces a FutureWarning:

StatisticMSAS.compute(
    real_data=(real_data['store_id'], real_data['nb_customers']),
    synthetic_data=(synthetic_data['store_id'], synthetic_data['nb_customers']),
    statistic='mean'
  )

FutureWarning: The provided callable <function mean at 0x79196b7fd000> is currently using SeriesGroupBy.mean. In a future version of pandas, the provided callable will be used directly. To keep current behavior pass the string "mean" instead.
  return df.groupby('keys')['values'].agg(stat_func)

The code should be updated so this warning doesn't surface.