Proxmox Mail Gateway display name is corrected (#3293)

Author: gringocl

frontend/public/json/proxmox-mail-gateway.json

@@ -1,5 +1,5 @@
 {
-    "name": "Promox Mail Gateway",
+    "name": "Proxmox Mail Gateway",
     "slug": "proxmox-mail-gateway",
     "categories": [
             1