build(plugin-theme-data): add copy script

Author: meteorlxy

packages/@vuepress/plugin-theme-data/package.json

@@ -25,7 +25,8 @@
   ],
   "scripts": {
     "build": "tsc -b tsconfig.build.json",
-    "clean": "rimraf lib *.tsbuildinfo"
+    "clean": "rimraf lib *.tsbuildinfo",
+    "copy": "cpx \"src/**/*.d.ts\" lib"
   },
   "dependencies": {
     "@vuepress/client": "2.0.0-alpha.24",