token-server: Bump GAE instance class.
token-server: Bump GAE instance class.

The token server will be on hot paths of requests that use delegation or
Swarming service accounts. It's response time matters.

R=nodir@chromium.org, iannucci@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2693603002

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go