Today Crystal 0.27.2 was released to address some bugs that existing in 0.27.1. We have added support for the new release and changed the Crystal runtimes on FaaStRuby.
Update the gem:
$ gem update faastruby
Existing functions that are configured with Crystal 0.27.1 should be updated to Crystal 0.27.2 and you can do that by editing faastruby.yml.
... runtime: "crystal:0.27.2" ...