Merge pull request #21 from emqx/doc_build

Fix doc dependencies security

docs/package.json

@@ -16,9 +16,6 @@
     "pdf": "npm run build:before && gitbook install && gitbook pdf . _book.pdf && npm run build:after"
   },
   "dependencies": {
-    "gitbook-cli": "^2.3.2",
-    "glob": "^7.1.3",
-    "node-xlsx": "^0.15.0",
-    "pangu": "^3.3.0"
+    "gitbook-cli": "^2.3.2"
   }
 }