cmd/tip: log error when fetching metadata

This error was previously ignored. This caused a silent failure when the
meta URL wasn't accessible.

Change-Id: I4020897ac15fec7b60a46277d81a99a6b6447a7d
Reviewed-on: https://go-review.googlesource.com/45655
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed