example/font: use an "example" build tag instead of "ignore".

The golang-dev discussion is at
https://groups.google.com/d/topic/golang-dev/qKpxZiNABcY/discussion

Change-Id: I55d626fd9b4c5585d11c585a8553fb5184d0ace7
Reviewed-on: https://go-review.googlesource.com/21788
Reviewed-by: Andrew Gerrand <adg@golang.org>
1 file changed