Ah we forgot about Travis Bintray has shut down, see: Announcing new apt and rpm repositories - The Crystal Programming Language
Further reading also at: Bintray will be gone at the end of April · Issue #10626 · crystal-lang/crystal · GitHub
Also consider this: The Travis CI Blog: ORG Shutdown
I’ll look into updating the Travis integration to use the new repositories.
Johannes actually thought of it, it’s just that nobody from Travis reacted to it in time: Update repository for crystal to OBS by straight-shoota · Pull Request #1987 · travis-ci/travis-build · GitHub