fix: package.json & package-lock.json to reduce vulnerabilities (#51)

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-FASTJSONPATCH-595663

Co-authored-by: Christoph Werner <[email protected]>

Author: snyk-bot

package-lock.json

@@ -19,7 +19,7 @@
     ],
     "license": "MIT",
     "dependencies": {
-        "fast-json-patch": "^2.0.4",
+        "fast-json-patch": "^2.2.1",
         "humps": "^2.0.1",
         "lodash": "^4.17.20",
         "mongoose": "^5.6.2"