UPGRADE.md - added flush cache requirement

framework/UPGRADE.md

@@ -16,12 +16,15 @@ php composer.phar global require "fxp/composer-asset-plugin"
 
 Upgrade from Yii 2.0.6
 ----------------------
-  
-* The signature of `yii\helpers\BaseInflector::transliterate()` was changed. The method is now public and has an extra optional parameter `$transliterator`.
-* If you override `yii\web\UrlRule` you have to know that the `pattern` matching group names are being replaced with the
-placeholders on class initialization to support wider range of allowed characters. If you implement `parseRequest()` or
-`createUrl()` and rely on parameter names, call `substitutePlaceholderNames()` in order to replace temporary IDs with
-parameter names after doing matching.
+
+* The signature of `yii\helpers\BaseInflector::transliterate()` was changed. The method is now public and has an
+extra optional parameter `$transliterator`.
+* In `yii\web\UrlRule` the `pattern` matching group names are being replaced with the placeholders on class
+initialization to support wider range of allowed characters. Because of this change:
+  - You are required to flush your application cache to remove outdated `UrlRule` serialized objects.
+  See the [Cache Flushing Guide](http://www.yiiframework.com/doc-2.0/guide-caching-data.html#cache-flushing)
+  - If you implement `parseRequest()` or `createUrl()` and rely on parameter names, call `substitutePlaceholderNames()`
+  in order to replace temporary IDs with parameter names after doing matching.
 
 
 Upgrade from Yii 2.0.5