oauth: fix formatting warnings reported by go vet

  oauth/oauth_test.go:158: possible formatting directive in Error call
  oauth/example/oauthreq.go:70: Println call ends with newline

LGTM=adg
R=golang-codereviews, bradfitz, adg
CC=golang-codereviews
https://codereview.appspot.com/106290044

Committer: Andrew Gerrand <adg@golang.org>
2 files changed