Bump nodemailer from 6.3.0 to 6.6.1 in /back-end

Bumps [nodemailer](https://github.com/nodemailer/nodemailer) from 6.3.0 to 6.6.1.
- [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/v6.3.0...v6.6.1)

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

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

back-end/package.json

@@ -22,7 +22,7 @@
     "helmet": "3.18.0",
     "ipfs-http-client": "32.0.1",
     "mongoose": "5.7.5",
-    "nodemailer": "6.3.0",
+    "nodemailer": "6.6.1",
     "nodemon": "1.19.1",
     "validator": "11.0.0",
     "web3": "^1.0.0-beta.55",

back-end/yarn.lock

@@ -3506,7 +3506,7 @@ minimist@0.0.8:
   resolved "https://registry.yarnpkg.com/minimist/-/minimist-0.0.8.tgz#857fcabfc3397d2625b8228262e86aa7a011b05d"
   integrity sha1-hX/Kv8M5fSYluCKCYuhqp6ARsF0=
 
-minimist@^1.2.0, minimist@^1.2.2:
+minimist@^1.2.0:
   version "1.2.2"
   resolved "https://registry.yarnpkg.com/minimist/-/minimist-1.2.2.tgz#b00a00230a1108c48c169e69a291aafda3aacd63"
   integrity sha512-rIqbOrKb8GJmx/5bc2M0QchhUouMXSpd1RTclXsB41JdL+VtnojfaJR+h7F9k18/4kHUsBFgk80Uk+q569vjPA==
@@ -3792,10 +3792,10 @@ nodeify@^1.0.1:
     is-promise "~1.0.0"
     promise "~1.3.0"
 
-nodemailer@6.3.0:
-  version "6.3.0"
-  resolved "https://registry.yarnpkg.com/nodemailer/-/nodemailer-6.3.0.tgz#a89b0c62d3937bdcdeecbf55687bd7911b627e12"
-  integrity sha512-TEHBNBPHv7Ie/0o3HXnb7xrPSSQmH1dXwQKRaMKDBGt/ZN54lvDVujP6hKkO/vjkIYL9rK8kHSG11+G42Nhxuw==
+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==
 
 nodemon@1.19.1:
   version "1.19.1"