Update OperatingSystem.php

Added windows 8.1 to operatingSystems array and osFamilies array.
Change name from windows 8 to 8.1

Change name from windows 8 to 8.1 where user_agent is Windows NT 6.3
Change name from windows 8 to 8.1

Change name from windows 8 to 8.1 where user_agent is Windows NT 6.3
Added regex

Added regex for detecting win8.1
Change the shortcode of windows 8.1 to 3 chars, now it W81 instead of WI8.1.
Added the shortcode to array:
https://github.com/n0f3x/device-detector/blob/master/DeviceDetector.php#L493
Merge pull request #5256 from N0F3X/master

Added windows8.1 detection