FIX: "The WebIO Jupyter extension was not detected"

[oyamad]

• https://github.com/QuantEcon/QuantEcon.notebooks/blob/master/recursive_repeated_games.ipynb
• https://nbviewer.org/github/QuantEcon/QuantEcon.notebooks/blob/master/recursive_repeated_games.ipynb

See also #88, #92.

[oyamad]

Also JuliaGizmos/WebIO.jl#381