This comes from IO::Socket not properly handling non-list values of the
nl-in property. This change came in with the recent refactor to make
encoders customizable in perl6 code.
I'm going to push a fix to rakudo soon.
It sounds like you're using a rakudo version that's not an official
release? That seems quite risky for a security-related program.
Anyway, with the "git checkout" command you can grab any version you
like. get a "commit" (a sha1 hash) from "git log" and "git checkout
cafe11112222" gives you the code as it was at that point, then configure
+ make + make install as usual. You may have to downgrade nqp and moarvm
to fit. For that, check out the files build/tools/NQP_REVISION inside
rakudo's repository and build/tools/MOAR_REVISION inside nqp's repository.