net/samplicator: fix fetch and bump to 1.3.8rc1

[Franco Fichtner]

Hi there,

This moves port fetch to GitHub and (unfortunately)
bumps to a newer version since there is no tag for
the former version.

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=212811

The new version was already tested in a production
environment and works as expected.  Can provide a
build log if requested.


Thanks,
Franco