[x/tour] go-tour: use time.Millisecond instead of raw constant
[x/tour] go-tour: use time.Millisecond instead of raw constant

R=adg
CC=golang-dev
https://golang.org/cl/11069043
X-Tour-Commit: aff2ab65e9fa1c7bbcfeb4d5918cca90bc90a40a

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website