Bump nodemailer from 4.6.8 to 6.4.16

Bumps [nodemailer](https://github.com/nodemailer/nodemailer) from 4.6.8 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@v4.6.8...v6.4.16)

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

Author: dependabot[bot]

package-lock.json

@@ -8,7 +8,7 @@
     "express-fileupload": ">=0.2.0",
     "axios": ">= 0.18.1",
     "node-cmd": ">= 3.0.0",
-    "nodemailer": ">= 4.0.0",
+    "nodemailer": ">= 6.4.16",
     "agentkeepalive": ">= 3.0.0",
     "sqlite3": "^4.0.6"
   },