added graceful-fs to patch fs

large vocabs couldn't be build due to the following error:
```
 Error: EMFILE: too many open files, scandir '....'
```

found the solution here:
<gatsbyjs/gatsby#12011>

gatsby-node.js

@@ -7,6 +7,8 @@ const jsonld = require('jsonld')
 const n3 = require('n3')
 const path = require('path')
 const fs = require('fs-extra')
+const gracefulFs = require('graceful-fs');
+gracefulFs.gracefulify(fs);
 const flexsearch = require('flexsearch')
 const omitEmpty = require('omit-empty')
 const urlTemplate = require('url-template')

package.json

@@ -24,6 +24,7 @@
     "gatsby-source-filesystem": "^2.1.37",
     "gatsby-transformer-json": "^2.2.17",
     "gatsby-transformer-sharp": "^2.3.3",
+    "graceful-fs": "^4.2.4",
     "jsonld": "^1.8.1",
     "koa": "^2.11.0",
     "koa-bodyparser": "^4.2.1",

src/webHookServer.js

@@ -4,6 +4,8 @@ const Router = require('koa-router')
 const bodyParser = require('koa-bodyparser')
 const uuidv4 = require('uuid/v4')
 const fs = require('fs-extra')
+const gracefulFs = require('graceful-fs');
+gracefulFs.gracefulify(fs);
 const exec = require('child_process').exec
 const fetch = require("node-fetch")