IE11 User Agent support added

Some of the most visible updates for IE11 involve the user-agent string. Here's what's reported for IE11 on Windows 8.1:

> Mozilla/5.0 (Windows NT 6.3; Trident/7.0; rv:11.0) like Gecko

Since MSIE string removed, CI detects IE11 as Mozilla 5.0. The easiest (but not the prettier) way to do this is to add rv as a new User Agent. For a better solution it has to preg_match "Trident" as a new if statement.