test-timers fail on maint-0.2.9

FAIL: src/test/test-timers

==========================

mean difference: 183123 usec

standard deviation: 524773.950303 usec

Either your system is under ridiculous load, or the timer backend is broken.

FAIL src/test/test-timers (exit status: 1)

https://travis-ci.org/torproject/tor/jobs/575709059#L2759

I wonder if this is a once-off, or if we haven't backported enough timer patches to 0.2.9.

I'll re-run the job, and see what happens.