build(deps): bump nodemailer in /apps/OpenSignServer

Bumps [nodemailer](https://github.com/nodemailer/nodemailer) from 6.9.14 to 6.9.15.
- [Release notes](https://github.com/nodemailer/nodemailer/releases)
- [Changelog](https://github.com/nodemailer/nodemailer/blob/master/CHANGELOG.md)
- [Commits](https://github.com/nodemailer/nodemailer/compare/v6.9.14...v6.9.15)

---
updated-dependencies:
- dependency-name: nodemailer
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

apps/OpenSignServer/package.json

@@ -38,7 +38,7 @@
     "multer": "^1.4.5-lts.1",
     "multer-s3": "^3.0.1",
     "node-forge": "^1.3.1",
-    "nodemailer": "^6.9.14",
+    "nodemailer": "^6.9.15",
     "parse": "^5.3.0",
     "parse-dbtool": "^1.2.0",
     "parse-server": "^7.2.0",