[docs] Fixed Windows build instructions (SRT ver).
[docs] Fixed Windows build instructions (SRT ver).

C++11 threads are available starting from v1.4.2
Cinegy/srt,Cinegy/srt,Haivision/srt,ethouris/srt,ethouris/srt,Haivision/srt,ethouris/srt,Cinegy/srt,ethouris/srt,Cinegy/srt,Haivision/srt,Haivision/srt