Switch the default branch to main

Switch the default branch from `master` to `main`, and update related URL links in README file.
For refer to https://github.blog/changelog/2020-10-01-the-default-branch-for-newly-created-repositories-is-now-main/

README.md

@@ -1,8 +1,8 @@
 # MD5
 
-[![GithubActions](https://img.shields.io/github/actions/workflow/status/xn-02f/md5/test.yml?style=flat-square&logo=github)](https://github.com/xn-02f/md5/actions)
+[![Actions](https://img.shields.io/github/actions/workflow/status/xn-02f/md5/test.yml?style=flat-square&logo=github)](https://github.com/xn-02f/md5/actions)
 [![npm](https://img.shields.io/npm/v/@xn-02f/md5.svg?style=flat-square&logo=npm)](https://www.npmjs.com/package/@xn-02f/md5)
-[![LICENSE](https://img.shields.io/github/license/xn-02f/md5.svg?style=flat-square&logo=opensourceinitiative)](https://github.com/xn-02f/md5/blob/master/LICENSE)
+[![LICENSE](https://img.shields.io/github/license/xn-02f/md5.svg?style=flat-square&logo=opensourceinitiative)](https://github.com/xn-02f/md5/blob/main/LICENSE)
 > 🔓 `MD5` is tiny library without dependencies for node, convert string to MD5 hash.
 
 ## Install
@@ -28,7 +28,7 @@ Parameter | return
 
 ### License
 
-> [MIT](https://github.com/xn-02f/md5/blob/master/LICENSE)
+> [MIT](https://github.com/xn-02f/md5/blob/main/LICENSE)
 
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