build: drop support for node 12 (#852)

BREAKING CHANGE: drop support for node 12

Author: Mister-Hope

docs/guide/getting-started.md

@@ -2,7 +2,7 @@
 
 ## Prerequisites
 
-- [Node.js v12+](https://nodejs.org/)
+- [Node.js v14+](https://nodejs.org/)
 - [Yarn v1 classic](https://classic.yarnpkg.com/en/) (Optional)
 
 ::: tip

docs/zh/guide/getting-started.md

@@ -2,7 +2,7 @@
 
 ## 依赖环境
 
-- [Node.js v12+](https://nodejs.org/)
+- [Node.js v14+](https://nodejs.org/)
 - [Yarn v1 classic](https://classic.yarnpkg.com/zh-Hans/) （可选）
 
 ::: tip

tsconfig.base.json

@@ -7,6 +7,6 @@
     "noEmitOnError": true,
     "noImplicitAny": false,
     "skipLibCheck": true,
-    "target": "ES2018"
+    "target": "ES2020"
   }
 }