tools: add mock-y js-yaml dependency to doctool

Add a hack js-yaml module to the doctool dependencies that simply
loads the one that’s included with eslint.

This helps avoiding to check in the whole dependency tree into
the core repo.

PR-URL: #6495
Reviewed-By: Robert Jefe Lindstaedt <robert.lindstaedt@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

Author: addaleax

tools/doc/node_modules/js-yaml/index.js

@@ -7,7 +7,8 @@
     "node": ">=0.6.10"
   },
   "dependencies": {
-    "marked": "~0.1.9"
+    "marked": "~0.1.9",
+    "js-yaml": "^3.5.2"
   },
   "devDependencies": {},
   "optionalDependencies": {},