Fix issues reported by go vet.

These issues were reported by `go vet` tool:

	google_oauth.go:106: possible formatting directive in Fatal call
	google_oauth.go:128: Println call ends with newline

The first one is clearly a bug but the second one might be intentional
to make the link stand out so I replaced the extra \n with another call
to `fmt.Println()`.
Merge pull request #9 from rce/go-vet-issues

Fix issues reported by go vet.