time: allow more time for TestOverflowRuntimeTimer to succeed
time: allow more time for TestOverflowRuntimeTimer to succeed

Attempting to fix windows gobuilders

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/13507044

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang