[webapi][XWALK-2939] Update 1 case for webaudio

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: [Tizen-IVI]
Unit test result summary: Pass 1, Fail 0, Blocked 0
Merge pull request #1354 from JianfengXu/webaudio/2939

[webapi][XWALK-2939] Update 1 case for webaudio