chore(): add p-limit to dependencies

Author: sgtcoolguy

packages/@vuepress/core/package.json

@@ -44,6 +44,7 @@
     "lru-cache": "^5.1.1",
     "mini-css-extract-plugin": "0.6.0",
     "optimize-css-assets-webpack-plugin": "^5.0.1",
+    "p-limit": "^3.0.1",
     "portfinder": "^1.0.13",
     "postcss-loader": "^3.0.0",
     "postcss-safe-parser": "^4.0.1",