Makefile: Don't use parallel "--no-notice"

Because it isn't available in all versions of GNU parallel (thanks to
Lewis Haley for the heads-up).

I had introduced this in e3aa9fd to avoid verbose output on Travis CI,
so I'll place the workaround in the Travis setup instead.
Merge pull request #189 from drothlis/travis-silence-parallel-citation-notice

Makefile: Don't use parallel "--no-notice"