Update TESTPACK.px

In Perl 5.20, CPANPLUS was removed
fix make testpack

fix following issues with Perl 5.20.0 and perl-cross 0.9

'''
./miniperl TESTPACK.px TESTPACK.list TESTPACK
Can't open cpan/Digest-MD5/README at TESTPACK.px line 143.

Can't open cpan/IO-Compress/examples: No such file or directory at TESTPACK.px line 159.
'''