Bump nodemailer from 4.7.0 to 6.6.1 in /backend

Bumps [nodemailer](https://github.com/nodemailer/nodemailer) from 4.7.0 to 6.6.1.
- [Release notes](https://github.com/nodemailer/nodemailer/releases)
- [Changelog](https://github.com/nodemailer/nodemailer/blob/master/CHANGELOG.md)
- [Commits](nodemailer/nodemailer@v4.7.0...v6.6.1)

---
updated-dependencies:
- dependency-name: nodemailer
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/package.json

@@ -80,7 +80,7 @@
     "node-broadlink": "^2.3.0",
     "node-orvibo-2": "^1.1.5",
     "node-yeelight-wifi": "^0.1.2",
-    "nodemailer": "4.7.0",
+    "nodemailer": "6.6.1",
     "path": "^0.12.7",
     "percent-normalizer": "^1.0.2",
     "promise-timeout": "^1.3.0",

backend/yarn.lock

@@ -4327,10 +4327,10 @@ node-yeelight-wifi@^0.1.2:
     node-ssdp "~4.0.0"
     portscanner "~2.2.0"
 
-nodemailer@4.7.0:
-  version "4.7.0"
-  resolved "https://registry.yarnpkg.com/nodemailer/-/nodemailer-4.7.0.tgz#4420e06abfffd77d0618f184ea49047db84f4ad8"
-  integrity sha512-IludxDypFpYw4xpzKdMAozBSkzKHmNBvGanUREjJItgJ2NYcK/s8+PggVhj7c2yGFQykKsnnmv1+Aqo0ZfjHmw==
+nodemailer@6.6.1:
+  version "6.6.1"
+  resolved "https://registry.yarnpkg.com/nodemailer/-/nodemailer-6.6.1.tgz#2a05fbf205b897d71bf43884167b5d4d3bd01b99"
+  integrity sha512-1xzFN3gqv+/qJ6YRyxBxfTYstLNt0FCtZaFRvf4Sg9wxNGWbwFmGXVpfSi6ThGK6aRxAo+KjHtYSW8NvCsNSAg==
 
 [email protected]:
   version "0.0.0"