fix(package): update vis-util to version 1.1.9 🚀 (#29)

This should greatly reduce prototype pollution.

* fix(package): update vis-util to version 1.1.9

* chore(package): update lockfile package-lock.json

Author: greenkeeper[bot]

package-lock.json

@@ -52,7 +52,7 @@
     "propagating-hammerjs": "1.4.7",
     "timsort": "0.3.0",
     "vis-data": "6.2.0",
-    "vis-util": "1.1.6"
+    "vis-util": "1.1.9"
   },
   "devDependencies": {
     "@babel/core": "^7.5.5",