correct mirror site links

MODEL_ZOO.md

@@ -20,7 +20,7 @@ Note: The train time was measured with PyTorch 0.4.1. We will update it later, w
 ## Mirror sites
 
 We use AWS as the main site to host our model zoo, and maintain a mirror on aliyun.
-You can replace `https://s3.ap-northeast-2.amazonaws.com` with `https://open-mmlab.oss-cn-beijing.aliyuncs.com` in model urls.
+You can replace `https://s3.ap-northeast-2.amazonaws.com/open-mmlab` with `https://open-mmlab.oss-cn-beijing.aliyuncs.com` in model urls.
 
 ## Common settings