depend to EU::MM 6.56.

16:23 chiba: ExtUtils-MakeMakerを6.48だと再現できて(inst_versionがundef)
16:23 chiba: 6.56にあげたら治りますた＞tokuhiro__

ref. http://github.com/tokuhirom/cpan-outdated/issues#issue/1

Makefile.PL

@@ -6,6 +6,7 @@ WriteMakefile(
         'LWP'      => 0,
         'IO::Zlib' => 0,
         'version'  => 0,
+        'ExtUtils::MakeMaker' => 6.56,
     },
     EXE_FILES => ['bin/cpan-outdated'],
 );