fix(app): Normalize flash type

Changed flash messages to use types provided by Bootstrap

Closes #16395

server/middlewares/flash-cheaters.js

@@ -16,7 +16,7 @@ export default function flashCheaters() {
       EXCLUDED_PATHS.indexOf(req.path) === -1 &&
       req.user && req.url !== '/' && req.user.isCheater
     ) {
-      req.flash('errors', {
+      req.flash('danger', {
         msg: dedent`
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