[webapi][XWALK-3118] Delete the excess character '\'

Remove the invalid charcter '\' from test code.
Impacted tests(approved):new 0,update 1,delete 0
Unit test platform:[android]
Unit test result summary:pass 1,fail 0,block 0
Merge pull request #1457 from chenxix/webapi/modify-color

[webapi][XWALK-3118] Delete the excess character '\'