tour: update to new favicon.ico
tour: update to new favicon.ico

Change favicon.ico to newer high resolution version from main project.

Change-Id: Iba9a5b13cb9615eaf10167a531065b9f8e101a71
Reviewed-on: https://go-review.googlesource.com/c/148037
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/tour,Go-zh/tour,dupoxy/go-tour-fr,dupoxy/go-tour-fr,zorion/go-tour-ca,zorion/go-tour-ca,dupoxy/go-tour-fr,Go-zh/tour,Go-zh/tour,Go-zh/tour