conf:format can't work

[byerose]

in plot_diagram.py
parser.add_argument('--format', default='png', help='overwrite the save figure format, pdf|png|jpg') will cause the format in the conf to fail.
should be
parser.add_argument('--format', help='overwrite the save figure format, pdf|png|jpg')

[guanyingc]

Hi, thanks for the bug report. Fix it in d73b62b.