fix doc version 8.1.0 link error (#114)

* fix doc version 8.1.0 link error

* fix chinese version 8.1.0 link error

docs/.vuepress/config.js

@@ -27,7 +27,7 @@ module.exports = {
         nav: [
           { text: "Home", link: "/" },
           { text: "Docs",  items: [
-            { text: '8.1.0', link: "https://github.com/apache/skywalking/tree/v8.0.1/docs"},
+            { text: '8.1.0', link: "https://github.com/apache/skywalking/tree/v8.1.0/docs"},
             { text: '8.0.1', link: "https://github.com/apache/skywalking/tree/v8.0.1/docs"},
             { text: '7.0.0', link: "https://github.com/apache/skywalking/tree/v7.0.0/docs"},
             { text: 'Nginx LUA 0.1.0', link: "https://github.com/apache/skywalking-nginx-lua/tree/v0.1.0"},
@@ -78,7 +78,7 @@ module.exports = {
           { text: "主页", link: "/zh/" },
           { text: "文档",
             items: [
-              { text: '8.1.0', link: "https://github.com/apache/skywalking/tree/v8.0.1/docs"},
+              { text: '8.1.0', link: "https://github.com/apache/skywalking/tree/v8.1.0/docs"},
               { text: '8.0.1', link: "https://github.com/apache/skywalking/tree/v8.0.1/docs"},
               { text: '7.0.0', link: "https://github.com/apache/skywalking/tree/v7.0.0/docs"},
               { text: 'Nginx LUA 0.1.0', link: "https://github.com/apache/skywalking-nginx-lua/tree/v0.1.0"},