Update nan requirement from 2.11.1 to 2.12.1 (#3767)

Updates the requirements on [nan](https://github.com/nodejs/nan) to permit the latest version.
- [Release notes](https://github.com/nodejs/nan/releases)
- [Changelog](https://github.com/nodejs/nan/blob/master/CHANGELOG.md)
- [Commits](https://github.com/nodejs/nan/commits/v2.12.1)

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

package.json

@@ -164,7 +164,7 @@
 		"mongodb": "3.1.10",
 		"monk": "6.0.6",
 		"ms": "2.1.1",
-		"nan": "2.11.1",
+		"nan": "2.12.1",
 		"nested-property": "0.0.7",
 		"nodemailer": "4.7.0",
 		"nprogress": "0.2.0",