[skip ci] Fixed broken links. (#3304)

Signed-off-by: NAmy Hong <yun.hong@zilliz.com>

README.md

-![Milvuslogo](https://github.com/milvus-io/docs/blob/v0.9.1/assets/milvus_logo.png)
+![Milvuslogo](https://github.com/milvus-io/docs/blob/master/v0.9.1/assets/milvus_logo.png)
 [![Slack](https://img.shields.io/badge/Join-Slack-orange)](https://join.slack.com/t/milvusio/shared_invite/zt-e0u4qu3k-bI2GDNys3ZqX1YCJ9OM~GQ)
 ![GitHub](https://img.shields.io/github/license/milvus-io/milvus)
 ![Docker pulls](https://img.shields.io/docker/pulls/milvusdb/milvus)
@@ -16,7 +16,7 @@ As an open source vector similarity search engine, Milvus is easy-to-use, highly
 
 The following is Milvus architecture:
 
-![arch](https://github.com/milvus-io/docs/blob/v0.9.1/assets/milvus_arch.png)
+![arch](https://github.com/milvus-io/docs/blob/master/v0.9.1/assets/milvus_arch.png)
 For more detailed introduction of Milvus and its architecture, see [Milvus overview](https://www.milvus.io/docs/overview.md). See Milvus [release notes](https://www.milvus.io/docs/release_notes.md) to keep up-to-date with its releases and updates.
 
 Milvus is an [LF AI Foundation](https://lfai.foundation/) incubation project. 

README_CN.md

 
-![Milvuslogo](https://github.com/milvus-io/docs/blob/v0.9.1/assets/milvus_logo.png)
+![Milvuslogo](https://github.com/milvus-io/docs/blob/master/v0.9.1/assets/milvus_logo.png)
 [![Slack](https://img.shields.io/badge/Join-Slack-orange)](https://join.slack.com/t/milvusio/shared_invite/zt-e0u4qu3k-bI2GDNys3ZqX1YCJ9OM~GQ)
 
 ![GitHub](https://img.shields.io/github/license/milvus-io/milvus)
@@ -21,7 +21,7 @@ Milvus 是一款开源的特征向量相似度搜索引擎，具有使用方便
 
 Milvus 的架构如下：
 
-![arch](https://github.com/milvus-io/docs/blob/v0.9.1/assets/milvus_arch.png)
+![arch](https://github.com/milvus-io/docs/blob/master/v0.9.1/assets/milvus_arch.png)
 
 若要了解 Milvus 详细介绍和整体架构，请访问 [Milvus 简介](https://www.milvus.io/docs/overview.md)。你可以通过 [版本发布说明](https://www.milvus.io/docs/release_notes.md) 获取最新版本的功能和更新。