Bump mongodb from 2.2.36 to 3.6.1 in /examples/todo-app/backend (#217)

Bumps [mongodb](https://github.com/mongodb/node-mongodb-native) from 2.2.36 to 3.6.1.
- [Release notes](https://github.com/mongodb/node-mongodb-native/releases)
- [Changelog](https://github.com/mongodb/node-mongodb-native/blob/master/CHANGES_3.0.0.md)
- [Commits](mongodb/node-mongodb-native@v2.2.36...v3.6.1)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

examples/todo-app/backend/package.json

@@ -9,7 +9,7 @@
   "license": "MIT",
   "dependencies": {
     "lodash": "^4.17.4",
-    "mongodb": "^2.2.30",
+    "mongodb": "^3.6.1",
     "uuid": "^2.0.3"
   },
   "devDependencies": {