Move the chutney pypy jobs to 0.4.2 xenial
Tor master will soon be unsupported on Travis xenial, because Travis xenial only has OpenSSL 1.1.0. (See legacy/trac#31820 (moved).)
So we need to move the pypy jobs to Tor 0.4.2 xenial, because pypy isn't packaged for Travis Bionic yet.