tour: Replacing Intn with Seed will not throw a random number

[mogwaipr]

Context: https://tour.golang.org/basics/1

I still cannot understand the documentation in order to properly use Seed to do random generation.

[ianlancetaylor]

CC @adg @campoy

If you are just asking a question, please use the golang-nuts mailing list or stack overflow. This issue tracker is for bug reports. Thanks.