tour: fix tour navigation for IE10, IE11, and Edge

IE browsers fire multiple events when href="". Workaround this issue by setting
href="#". Also prevent default click event from firing.

Fixes golang/go#12084

Change-Id: I09410bd9f491edc03af8b093b640755c5ebf8b84
Reviewed-on: https://go-review.googlesource.com/15000
Reviewed-by: Andrew Gerrand <adg@golang.org>
2 files changed