解决host.robots.ox.ac.uk打不开无法下载voc2007和voc2012问题

使用镜像替代

http://data.brainchip.com/dataset-mirror/voc/

用上面替换下面

http://host.robots.ox.ac.uk/pascal/VOC/voc2012

常用链接，复制下载
'devkit': 'http://data.brainchip.com/dataset-mirror/voc/VOCdevkit_18-May-2011.tar',
'trainval_2007': 'http://data.brainchip.com/dataset-mirror/voc/VOCtrainval_06-Nov-2007.tar',
'test_images_2007': 'http://data.brainchip.com/dataset-mirror/voc/VOCtest_06-Nov-2007.tar',
'test_anno_2007': 'http://data.brainchip.com/dataset-mirror/voc/VOCtestnoimgs_06-Nov-