for #367, update wiki to v3

 # the config for srs to support nginx-rtmp exec.
-# @see https://github.com/simple-rtmp-server/srs/wiki/v2_CN_NgExec
+# @see https://github.com/simple-rtmp-server/srs/wiki/v3_CN_NgExec
 # @see full.conf for detail config.
 
 listen              1935;