indentation in toolbar example

[msseibel]

Please fix indentation:
kv = """
BoxLayout:
orientation: 'vertical'

MatplotFigure:
    id: figure_wgt
    size_hint: 1, 0.7

MatplotNavToolbar:
    id: navbar_wgt
    size_hint: 1, 0.3
    figure_widget: figure_wgt

"""