doc: update the minimum required version of Go

Author: panjf2000

README.md

@@ -4,7 +4,7 @@
 <a title="Build Status" target="_blank" href="https://github.com/panjf2000/gnet/actions?query=workflow%3ATests"><img src="https://img.shields.io/github/actions/workflow/status/panjf2000/gnet/test.yml?branch=dev&style=flat-square&logo=github-actions" /></a>
 <a title="Codecov" target="_blank" href="https://codecov.io/gh/panjf2000/gnet"><img src="https://img.shields.io/codecov/c/github/panjf2000/gnet?style=flat-square&logo=codecov" /></a>
 <a title="Supported Platforms" target="_blank" href="https://github.com/panjf2000/gnet"><img src="https://img.shields.io/badge/platform-Linux%20%7C%20FreeBSD%20%7C%20DragonFly%20%7C%20Darwin%20%7C%20Windows-549688?style=flat-square&logo=launchpad" /></a>
-<a title="Require Go Version" target="_blank" href="https://github.com/panjf2000/gnet"><img src="https://img.shields.io/badge/go-%3E%3D1.9-30dff3?style=flat-square&logo=go" /></a>
+<a title="Require Go Version" target="_blank" href="https://github.com/panjf2000/gnet"><img src="https://img.shields.io/badge/go-%3E%3D1.13-30dff3?style=flat-square&logo=go" /></a>
 <br />
 <a title="Chat Room" target="_blank" href="https://gitter.im/gnet-io/gnet?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=body_badge"><img src="https://badges.gitter.im/gnet-io/gnet.svg" /></a>
 <a title="Go Report Card" target="_blank" href="https://goreportcard.com/report/github.com/panjf2000/gnet"><img src="https://goreportcard.com/badge/github.com/panjf2000/gnet?style=flat-square" /></a>

README_ZH.md

@@ -4,7 +4,7 @@
 <a title="Build Status" target="_blank" href="https://github.com/panjf2000/gnet/actions?query=workflow%3ATests"><img src="https://img.shields.io/github/actions/workflow/status/panjf2000/gnet/test.yml?branch=dev&style=flat-square&logo=github-actions" /></a>
 <a title="Codecov" target="_blank" href="https://codecov.io/gh/panjf2000/gnet"><img src="https://img.shields.io/codecov/c/github/panjf2000/gnet?style=flat-square&logo=codecov" /></a>
 <a title="Supported Platforms" target="_blank" href="https://github.com/panjf2000/gnet"><img src="https://img.shields.io/badge/platform-Linux%20%7C%20FreeBSD%20%7C%20DragonFly%20%7C%20Darwin%20%7C%20Windows-549688?style=flat-square&logo=launchpad" /></a>
-<a title="Require Go Version" target="_blank" href="https://github.com/panjf2000/gnet"><img src="https://img.shields.io/badge/go-%3E%3D1.9-30dff3?style=flat-square&logo=go" /></a>
+<a title="Require Go Version" target="_blank" href="https://github.com/panjf2000/gnet"><img src="https://img.shields.io/badge/go-%3E%3D1.13-30dff3?style=flat-square&logo=go" /></a>
 <br />
 <a title="Chat Room" target="_blank" href="https://gitter.im/gnet-io/gnet?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=body_badge"><img src="https://badges.gitter.im/gnet-io/gnet.svg" /></a>
 <a title="Go Report Card" target="_blank" href="https://goreportcard.com/report/github.com/panjf2000/gnet"><img src="https://goreportcard.com/badge/github.com/panjf2000/gnet?style=flat-square" /></a>