fix column name in the UpdateServer query

internal/server.sql

@@ -43,7 +43,7 @@ SELECT version_code::varchar, cnt::bigint from count_servers_by_version_code() r
 -- name: UpdateServer :one
 UPDATE servers
 SET
-    config = coalesce(sqlc.narg('open'), open)
+    open = coalesce(sqlc.narg('open'), open)
 WHERE key = sqlc.arg('key')
 RETURNING *;