Just made small trial on CircleCI and elixir combination, and taking some notes here.
Though the CircleCI doesn’t have latest erlang/elixir installed, it can be installed as the custom configuration through circle.yml. It takes some time initially, but applying cache makes it pretty much fast for normal code deployments.
Comparing with TravisCI, detection of updates in GitHub and build processing seems pretty much fast, though there’s no free version on CircleCI. It may be a good option for private repositories.
The configuration is messy, but the following is the working example with very simple elixir codes (tested on erlang 17.0 and elixir v0.14.2-dev).