Version 1.4.0

See merge request !139

Mark Redis experimental while we sort out bugs

See merge request !138

Temporary measure so we can cut a release from master while some Redis
integration issues are still being sorted out.

https://gitlab.com/gitlab-org/gitlab-workhorse/issues/113

https://gitlab.com/gitlab-org/gitlab-workhorse/merge_requests/136

Add metrics for queueing mechanism

See merge request !122

Add apiCiLongPolling option to use a new redis queueing mechanism

See merge request !128

Rename gitlab_workhorse_builds_register_handler_hits to gitlab_workhorse_builds_register_handler_requests

Update Go used for testing to 1.6.4 1.7.5 and add 1.8.0

See merge request !135