Bump mongodb from 2.2.36 to 3.1.13 in /behavioral_experiments

Bumps [mongodb](https://github.com/mongodb/node-mongodb-native) from 2.2.36 to 3.1.13.
- [Release notes](https://github.com/mongodb/node-mongodb-native/releases)
- [Changelog](https://github.com/mongodb/node-mongodb-native/blob/3.6/CHANGES_3.0.0.md)
- [Commits](mongodb/node-mongodb-native@v2.2.36...v3.1.13)

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Author: dependabot[bot]

behavioral_experiments/package-lock.json

@@ -16,7 +16,7 @@
     "lodash": "^4.17.21",
     "minimist": "^1.2.5",
     "mkdirp": "^0.5.1",
-    "mongodb": "^2.2.35",
+    "mongodb": "^3.1.13",
     "request": "^2.87.0",
     "socket.io": "^2.4.1",
     "socket.io-client": "^2.2.0",