Merge pull request #8323 from steveklabnik/changelog_7997

Add changelog for #7997.

actionpack/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Add i18n scope to disance_of_time_in_words. *Steve Klabnik*
+
 *   `assert_template`:
     - is no more passing with empty string.
     - is now validating option keys. It accepts: `:layout`, `:partial`, `:locals` and `:count`.