Remove deprecated usage of Series.nonzero()

Series.nonzero() was deprecated in pandas-dev/pandas#24048.

Using the latest pandas breaks fbprophet.

We can replace .nonzero() use with .to_numpy().nonzero().

Author: charignon

python/fbprophet/forecaster.py

@@ -942,7 +942,7 @@ def set_auto_seasonalities(self):
         first = self.history['ds'].min()
         last = self.history['ds'].max()
         dt = self.history['ds'].diff()
-        min_dt = dt.iloc[dt.values.nonzero()[0]].min()
+        min_dt = dt.iloc[dt.values.to_numpy().nonzero()[0]].min()
 
         # Yearly seasonality
         yearly_disable = last - first < pd.Timedelta(days=730)