linux.sigplain111 test failed on Travis

https://travis-ci.com/DynamoRIO/dynamorio/jobs/243628854

720 65/314 Test  #62: code_api|linux.sigplain111 .......................................***Failed  Required regular expression not found.Regex=[^Sending SIGUSR2
721Sending SIGUSR1
722in signal handler
7231750007\.722714
724Got some timer hits!
725$
726]  0.94 sec
727Sending SIGUSR2
728Sending SIGUSR1
729in signal handler
730Got some timer hits!