fix(security): updated mongodb dependency due to vulnerabilities

[winstonralph]

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Summary
Version 3.6.11 of MongoDB is getting flagged by our security scans (White Hat) as having the following vulnerabilities:

Medium: VULNDB-210509
Medium: VULNDB-228951
Medium: VULNDB-243320
High: VULNDB-243321
Medium: VULNDB-243324
Medium: VULNDB-243343
High: VULNDB-243412
Medium: VULNDB-243413
Medium: VULNDB-250889
Medium: VULNDB-262684

Examples

Only involves MongoDB version change. We have tested this within our own project without issues.

[vkarpov15]

LGTM, except for the version bump. The only feature change in mongodb@3.7 is this one: https://github.com/mongodb/node-mongodb-native/pull/2850/files, which should be sufficiently minor to only require a patch release for Mongoose.