fix: upgrade mongoose from 6.11.1 to 6.12.6

Snyk has created this PR to upgrade mongoose from 6.11.1 to 6.12.6.

See this package in npm:
https://www.npmjs.com/package/mongoose

See this project in Snyk:
https://app.snyk.io/org/nc-minh/project/2be35f06-8317-474e-b72a-1e47f55c131f?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot