fix detail url (open-mmlab#267)

Author: yamengxi

docs/getting_started.md

@@ -115,7 +115,7 @@ The training and validation set of Pascal Context could be download from [here](
 
 To split the training and validation set from original dataset, you may download trainval_merged.json from [here](https://codalabuser.blob.core.windows.net/public/trainval_merged.json).
 
-If you would like to use Pascal Context dataset, please install [Detail](https://github.com/ccvl/detail-api) and then run the following command to convert annotations into proper format.
+If you would like to use Pascal Context dataset, please install [Detail](https://github.com/zhanghang1989/detail-api) and then run the following command to convert annotations into proper format.
 
 ```shell
 python tools/convert_datasets/pascal_context.py data/VOCdevkit data/VOCdevkit/VOC2010/trainval_merged.json