FigureWidget doesn't update in Jupyter Notebook

This snippet in a Python cell produces a chart, but the chart does not update to get the new title and new data.

import plotly.graph_objs as go
from plotly.offline import download_plotlyjs, init_notebook_mode, plot, iplot

init_notebook_mode()
data = [go.Bar(
            x=['giraffes', 'orangutans', 'monkeys'],
            y=[20, 14, 23]
    )]
layout = {'yaxis': {'range': [0, 25]}}
fig = go.FigureWidget(data, layout)
iplot(fig)

# The following code is ignored.
fig.data[0].y = (5,10,1)
fig.layout.title = "New title"

Plotly version: 3.5.0
Server Information:
You are using Jupyter notebook.
The version of the notebook server is: 5.7.4
The server is running on this version of Python:
Python 3.7.1 (default, Dec 14 2018, 13:28:58)
[Clang 4.0.1 (tags/RELEASE_401/final)]

Current Kernel Information:
Python 3.7.1 (default, Dec 14 2018, 13:28:58)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.2.0 -- An enhanced Interactive Python. Type '?' for help.

Run the provided Python snippet in a Jupyter Notebook with the reported Plotly and notebook versions, then inspect the FigureWidget and iplot entry points involved in displaying it. Done means that changing fig.data[0].y and fig.layout.title updates the displayed chart with the new data and title.