fix(package): update mongoose to version 5.9.7

Closes #99

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
     "helmet": "^3.15.0",
     "iconv-lite": "0.5.0",
     "jsonwebtoken": "8.4.0",
-    "mongoose": "5.5.13",
+    "mongoose": "5.9.7",
     "morgan": "1.9.1",
     "nodemon": "1.19.1",
     "passport": "^0.4.0",