FIX: comment out pyo.init_notebook_mode to fix PDF build (#309)

pyo.init_notebook_mode(connected=True) outputs only text/html which the
LaTeX builder cannot render. With -W (warnings-as-errors) this kills the
PDF build. The lecture uses kaleido for static PNG export so this call is
not needed for the book build.

Closes #308

Author: mmcky

lectures/knowing_forecasts_of_others.md

@@ -921,7 +921,8 @@ import plotly.offline as pyo
 from statsmodels.regression.linear_model import OLS
 from IPython.display import display, Latex, Image
 
-pyo.init_notebook_mode(connected=True)
+# Uncomment the following line when running in a notebook
+# pyo.init_notebook_mode(connected=True)
 ```
 
 ```{code-cell} python3