Fix Version Check for IE11

IE 11 does not have MSIE string in user agent, so check for IE 8 causes it to break pages showing on IE 11. Check makes sure MSIE before comparing against IE 8
Carousel: Update IE browser check

Updates the IE browser check to utilize WordPress core functions instead of
attempting to test the browser agent string, which has changed format in
IE 11. This commit closes #172 and creates a new PR for the functionality
Carousel: Final tested fix for IE 11
Merge pull request #445 from Automattic/ie_versions

  Carousel: fix Version Check for IE11 take 2