* ci: switch to go1.12.12 on machine executors

- This brings in recent ci changes from the release/1.2.x branch.

* go mod vendor

* ci: remove ent build tags

* ci: fix gopath

* go mod vendor

* ci: ensure yarn install

* ci: add debug commands

* ci: debugging

* ci: increment yarn cache; remove debugging

* ci: remove redundant yarn install