Makefile.sub: fix typo

* win32/Makefile.sub (MISSING): fix typo, missing extention.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43417 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-10-25

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43418 b2dd03c8-39d4-4d8f-98ff-823fe69b080e