Update mocha to fix js-yaml vulnerability

Author: rylnd

package-lock.json

@@ -38,7 +38,7 @@
     "@types/serve-favicon": "^2.2.30",
     "chai": "^4.2.0",
     "concurrently": "^4.1.0",
-    "mocha": "^6.1.3",
+    "mocha": "^6.1.4",
     "onchange": "^5.2.0",
     "prettier": "^1.17.0",
     "serve-favicon": "^2.5.0",