[webapi][XWALK-428]Fix grammar issue for alarm

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: [Tizen IVI]
Test result summary: Pass 1, Fail 0, Blocked 0
Merge pull request #430 from JianfengXu/xujf/webapi/alarm

[webapi][XWALK-428]Fix logic issue for alarm