chore(package): update @types/mongoose to version 5.5.20

Closes #101

Author: greenkeeper[bot]

package.json

@@ -32,7 +32,7 @@
     "@types/express": "4.17.0",
     "@types/mocha": "^5.2.7",
     "@types/mongodb": "^3.1.14",
-    "@types/mongoose": "5.5.7",
+    "@types/mongoose": "5.5.20",
     "@types/morgan": "^1.7.32",
     "@types/node": "12.0.5",
     "@types/passport": "1.0.0",