Pie chart don't work out of the box #4

Hi,

Same issue with pie chart :
print series_json = [{"data": [{"data": 2, "label": "Bureau"}, {"data": 1, "label": "Atelier"}, {"data": 1, "label": "Commerce"}, {"data": 1, "label": "Stockage"}]}]

but should be :
[{"data": 2, "label": "Bureau"}, {"data": 1, "label": "Atelier"}, {"data": 1, "label": "Commerce"}, {"data": 1, "label": "Stockage"}]

I can see a a graph with :
var plot = $.plot(placeholder, {{ graph.series_json|safe }}[0]['data'], options);