See e.g.
https://travis-ci.org/klenin/cats-problem/jobs/560916865
Files like
https://storage.googleapis.com/travis-ci-language-archives/perl/binaries/ubuntu/16.04/x86_64/perl-5.20.tar.bz2
are not available any more for some reason.
See Failure with Perl 5.16, 5.18 & 5.20
Likely caused by dist: xenial becoming the implicit default, and you need to add dist: trusty to regain access to those old versions of perl.
This helped, thanks
Just wanted to mention that, as @jayvdb said, it’s most probably a side-effect of the migration to Xenial as our default distribution.
We have also updated on Xenial documentation to mention which Perl versions are supported. See https://docs.travis-ci.com/user/reference/xenial#perl-support.
Hope this helps!