Set minimum version for open prereq

I've got some errors from CPANTesters. All from OpenBSD with Perl
5.10.0. It seems that this has to do with the open module version,
which was bumped from 1.06 to 1.07 at Perl 5.10.1. So, I'm fixing the
prereq dependency at version 1.07, admittedly a lame attempt at a
solution.