[#30790] fix JHtmlBehavior::noframes()

Fixing issue described in [bug #30790](http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_id=8103&tracker_item_id=30790), related to header typo (libraries/cms/html/behavior.php)
Correct header name is X-Frame-Options not X-Frames-Options as stated in [the docs](https://developer.mozilla.org/en-US/docs/HTTP/X-Frame-Options)