Installing InlineX::CPP2XS: Test::warn dependency issue

[David Oswald]

There's what I think is probably just a typo in Makefile.PL for InlineX::CPP2XS

The prereq for Test::Warn is specified as Test::warn

This causes cpanm to fail to install InlineX::CPP2XS, since it treats
module names case-sensitively (as it should).

Dave