Pick up the bug fix for golang/oauth2#237
Bump up cloud.google.com/go as a result of updating the OAuth2 code.

This commit was generated by:
./hack/pin-dependency.sh golang.org/x/oauth2 9f3314589c9a
./hack/pin-dependency.sh cloud.google.com/go v0.34.0
./hack/update-vendor.sh
git add vendor
git add -u