button does not toggle with keyboard shortcuts

[yoichi-kazama]

Keyboard shortcuts P for pan and O for zoom work fine, but they do not trigger button toggle.

To reproduce:

1. show an ipympl plot on Jupyterlab
2. click on the figure to focus
3. push 'P' for pan; the cursor changes but the button does not

Firefox 67.0.4, Windows 8.1

jupyterlab                1.0.1                    py37_0    conda-forge
jupyterlab_server         1.0.0                      py_0
matplotlib                3.1.1                    py37_0    conda-forge
matplotlib-base           3.1.1            py37h2852a4a_0    conda-forge
ipympl                    0.3.2                      py_0    conda-forge
ipywidgets                7.5.0                      py_0    conda-forge