Are you sure you're running Windows Phone 8.1 Update 1 (that was released yesterday)? My 930 is still running 8.1 without update 1 and it still ends with "like Gecko." My friend's 920 with update 1, on the other hand, is now using the same user agent as in the blog post.

For a reference (settings → about), the version on the second line is the one with the new UA:

    Windows Phone 8.1 (OS version 8.10.12397.895)
    Windows Phone 8.1 Update (OS version 8.10.14147.180)