use another cdn for sockjs_url option
use another cdn for sockjs_url option

It seems that SockJS CDN will be removed with 1.0 release - https://github.com/sockjs/sockjs-client/issues/198
codepython/sockjs-tornado,pjknkda/sockjs-tornado,codepython/sockjs-tornado,barseghyanartur/sockjs-tornado,MrJoes/sockjs-tornado,pjknkda/sockjs-tornado,ImaginationForPeople/sockjs-tornado,ImaginationForPeople/sockjs-tornado,ImaginationForPeople/sockjs-tornado,pjknkda/sockjs-tornado,mrjoes/sockjs-tornado,DexterInd/sockjs-tornado,DexterInd/sockjs-tornado,codepython/sockjs-tornado,DexterInd/sockjs-tornado