fix Kamal secret

Author: mythz

config/deploy.yml

@@ -6,8 +6,10 @@ image: my-user/myapp
 
 # Required for use of ASP.NET Core with Kamal-Proxy.
 env:
-  ASPNETCORE_FORWARDEDHEADERS_ENABLED: true
-  SERVICESTACK_LICENSE: $SERVICESTACK_LICENSE
+  clear:
+    ASPNETCORE_FORWARDEDHEADERS_ENABLED: true
+  secret:
+    - SERVICESTACK_LICENSE
 
 # Deploy to these servers.
 servers: