Bump nodemailer from 2.7.2 to 6.4.16

Bumps [nodemailer](https://github.com/nodemailer/nodemailer) from 2.7.2 to 6.4.16.
- [Release notes](https://github.com/nodemailer/nodemailer/releases)
- [Changelog](https://github.com/nodemailer/nodemailer/blob/master/CHANGELOG.md)
- [Commits](nodemailer/nodemailer@v2.7.2...v6.4.16)

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

Author: dependabot[bot]

package-lock.json

@@ -40,7 +40,7 @@
     "multer-gridfs": "0.0.1",
     "multer-gridfs-storage": "0.0.5",
     "natives": "^1.1.6",
-    "nodemailer": "^2.6.4",
+    "nodemailer": "^6.4.16",
     "passport": "~0.1.17",
     "passport-local": "~0.1.6",
     "serve-favicon": "^2.3.2",