Yarn has been updated to v0.27.5. You can see this announcement here.
You can subscribe to notifications for announcements like this via the Announcements Category on CircleCI Discuss.
How we’re going about CircleCI 1.0 image updates:
There are currently two build images for CircleCI 1.0. The Ubuntu 14.04 image and the Ubuntu 12.04 image. The 12.04 image has been End of Life’d (EOL) by Canonical and thus, we have EOL’d it too. We will not be updating that image. The Ubuntu 14.04 image will be updated for awhile though there isn’t set dates. Typically in the past, this has been updated once a quarter. We suggest for more frequent updates and full control of your build, to use CircleCI 2.0.
TL:DR;
Ubuntu 12.04 - will not ever be updated
Ubuntu 14.04 - software updated for major versions and security/bug fixes approximately once a quarter
CircleCI 2.0 - Use this for more control on when and what is updated