Security: update package use of mongodb library

[camsjams]

There is an advisory for the npm package mongodb that can be solved by upgrading to the 3.x version of v3.13.13 or higher.

By upgrading, these issues should be fixed:

Denial of Service

• NPM advisory 1203
• SNYK-JS-MONGODB-473855

Should be fixed by #83 and #76

[camsjams]

Looks to be fixed on latest version via changes from #83, with package versions at:

"mongodb": "3.3.5",
"sharedb-mongo": "1.0.0-beta.11"

For anyone using this library, you can upgrade to the above at minimum to solve these advisories.