also check for -f in bin/scan_prereqs
don't use lib $Bin/../lib
Problem: use CPAN::Meta::Requirements 2.124
core module 2.122 is installed in
.../perl-5.18.2/lib/5.18.2/CPAN/Meta/Requirements.pm
2.124 gets installed in
.../perl-5.18.2/lib/site_perl/5.18.2/CPAN/Meta/Requirements.pm

use lib $Bin/../lib now puts the first one at the beginning
of @INC.
As a result:
CPAN::Meta::Requirements version 2.124 required--this is only version 2.122