Fixed reference path in eventsource-constructor-url-multi-window.htm

https://bugzilla.mozilla.org/show_bug.cgi?id=869865

Signed-off-by: wanmingx.lin <wanmingx.lin@intel.com>
Merge pull request #264 from zqzhang/submission/zqzhang/fixing-eventsource-constructor-url-multi-window

Fixed reference path in eventsource-constructor-url-multi-window.htm