fix: package.json & .snyk to reduce vulnerabilities

The following vulnerabilities are fixed with a Snyk patch:
- https://snyk.io/vuln/npm:moment:20170905

Latest report for web-innovate/leave-tracking:
https://snyk.io/test/github/web-innovate/leave-tracking

.snyk

@@ -0,0 +1,8 @@
+# Snyk (https://snyk.io) policy file, patches or ignores known vulnerabilities.
+version: v1.8.0
+ignore: {}
+# patches apply the minimum changes required to fix a vulnerability
+patch:
+  'npm:moment:20170905':
+    - aurelia-chart > chart.js > moment:
+        patched: '2017-12-01T01:59:14.848Z'

package.json

@@ -5,9 +5,13 @@
   "scripts": {
     "install": "cd ./frontend && yarn install && cd ../backend && yarn install",
     "build": "cd ./frontend && au build --env prod && cd ../backend && gulp",
-    "lint": "cd ./backend && yarn lint"
+    "lint": "cd ./backend && yarn lint",
+    "snyk-protect": "snyk protect",
+    "prepublish": "npm run snyk-protect"
   },
   "dependencies": {
-    "yarn": "^0.22.0"
-  }
+    "yarn": "^0.22.0",
+    "snyk": "^1.52.1"
+  },
+  "snyk": true
 }