Update go version to 1.11 in circle tests. (#10212)
Update go version to 1.11 in circle tests. (#10212)

* Update go version to 1.11 in circle tests.

New image with go1.11 had been pushed. This is also done to master in
https://github.com/istio/istio/pull/10186 to resolve some linter
problems.

Also we had recently updated the go version to 1.11 in the dev guide.
https://github.com/istio/istio/wiki/Dev-Guide

* Fix linter problem due to go version change

istio/istio,istio/istio,geeknoid/istio,smawson/istio,istio/istio,geeknoid/istio,istio/istio,smawson/istio,geeknoid/istio,geeknoid/istio,istio/istio,geeknoid/istio,smawson/istio,smawson/istio,geeknoid/istio,smawson/istio,smawson/istio