Add Mailhog to utility resources

CONTRIBUTORS.md

@@ -5,4 +5,5 @@ These are lovely people who have helped this project:
   * twitter: @lostdesign
 - [Kevin](https://github.com/S3B4S) :dog:
 - [jacobparis](https://github.com/jacobparis) : Team Devcord
-  * twitter: @jacobmparis
+  * twitter: @jacobmparis
+- [JonasPardon](https://github.com/JonasPardon)

resources/utility.json

@@ -163,6 +163,12 @@
       "desc": "Let's Encrypt is a free, automated, and open certificate authority brought to you by the non-profit Internet Security Research Group (ISRG).",
       "url": "https://letsencrypt.org/",
       "tags": []
+    },
+    {
+      "title": "Mailhog",
+      "desc": "Web and API based SMTP testing.",
+      "url": "https://github.com/mailhog/MailHog",
+      "tags": []
     }
   ]
-}
+}