* ext/socket/extconf.rb ($distcleanfiles): fixed typo.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@21738 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/socket/extconf.rb

@@ -298,7 +298,7 @@ end
 have_header("sys/un.h")
 have_header("sys/uio.h")
 
-$distcleanfiles.concat << "constants.h" << "constdefs.*"
+$distcleanfiles << "constants.h" << "constdefs.*"
 
 if have_func(test_func)
   have_func("hsterror")