Bump debug from 2.6.9 to 4.1.1 (#68)

Bumps [debug](https://github.com/visionmedia/debug) from 2.6.9 to 4.1.1.
- [Release notes](https://github.com/visionmedia/debug/releases)
- [Commits](debug-js/debug@2.6.9...4.1.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -51,7 +51,7 @@
     "benchmark": "^2.0.0",
     "bson": "^1.0.5",
     "coveralls": "^2.11.2",
-    "debug": "^2.2.0",
+    "debug": "^4.1.1",
     "eslint-config-mongodb-js": "^5.0.3",
     "istanbul": "^0.4.5",
     "mocha": "^3.1.2",