Fixed slashed to match guide

framework/i18n/I18N.php

@@ -32,7 +32,7 @@ class I18N extends Component
      * for creating the [[MessageSource]] objects.
      *
      * The message category patterns can contain the wildcard '*' at the end to match multiple categories with the same prefix.
-     * For example, 'app\*' matches both 'app\cat1' and 'app\cat2'.
+     * For example, 'app/*' matches both 'app/cat1' and 'app/cat2'.
      *
      * The '*' category pattern will match all categories that do not match any other category patterns.
      *