Use securestring for passwords

templates/arm/deployment.json.erb

@@ -11,7 +11,7 @@
     },
     <% if operating_system == 'Windows' %>
     "adminPassword": {
-      "type": "string",
+      "type": "securestring",
       "metadata": {
         "description": "Password for the Virtual Machine (only used on Windows)"
       }