chore: add docs:build script

Author: yyx990803

.gitignore

@@ -3,3 +3,4 @@ exploration
 node_modules
 *.log
 example/dist
+docs/.vuepress/dist

package.json

@@ -10,6 +10,7 @@
     "build": "webpack --config example/webpack.config.js --hide-modules",
     "dev": "webpack-dev-server --config example/webpack.config.js --inline --hot",
     "docs": "vuepress dev docs",
+    "docs:build": "vuepress build docs",
     "prepublishOnly": "conventional-changelog -p angular -r 2 -i CHANGELOG.md -s"
   },
   "author": "Evan You",