tour: use uint in example code to avoid amiguity with inline code

Fixes go/golang#13412

Change-Id: I8900638c707120832e2d5a1e5c3be2c14baef6a5
Reviewed-on: https://go-review.googlesource.com/17513
Reviewed-by: Minux Ma <minux@golang.org>
2 files changed