Avoid mixed space / tabs indentation
Avoid mixed space / tabs indentation

ipython/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,SylvainCorlay/ipywidgets,ipython/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets