Comment 2 for bug 1727021

The new default image has been delayed a bit, and is now due November 28th, see https://blog.travis-ci.com/2017-10-16-a-new-default-os-x-image-is-coming for details. I'll experiment a bit with this image, because I believe we can drop the workaround with `brew update`. I'll keep the branch open untill the new image is default though, because I need to override the currently default image (7.3). Once the new image is default, it will no longer be neccessary to override it, so we can drop the osx_image line from the yml config.