I can see this in your failing build:
Warning: Your Xcode (8.3.3) is outdated. Please update to Xcode 9.2 (or delete it). Xcode can be updated from the App Store. Warning: A newer Command Line Tools release is available. Update them from Software Update in the App Store.
Can you try to run your build on Xcode 9.2 with the following in your .travis.yml file?
I would even recommend using a newer image. You can look at your supported images here:
Let us know how it goes!
Nice catch, @dominic, I missed that!
In the light of this, the more concerning message is https://travis-ci.org/olbat/icu.cr/jobs/596330893#L3743-L3745:
Warning: You are using macOS 10.12. We (and Apple) do not provide support for this old version. You will encounter build failures with some formulae.
Which means that Homebrew has stopped providing newer bottles for OSX 10.12 and @olbat needs to rather update to 10.13 i.e.
(which is the default so they can omit the clause altogether)
Awesome, it worked!
Thanks a lot for your help on this