Add missing dependency

Author: wooorm

package.json

@@ -40,6 +40,7 @@
     "nlcst-to-string": "^3.0.0",
     "repeat-string": "^1.0.0",
     "unist-util-position": "^4.0.0",
+    "vfile": "^5.0.0",
     "vfile-location": "^4.0.0"
   },
   "devDependencies": {