* lib/rubygems/resolver.rb: fix error of null device reference with DOSISH

platform.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51095 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Thu Jul  2 09:51:44 2015  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
+
+	* lib/rubygems/resolver.rb: fix error of null device reference with DOSISH
+	  platform.
+
 Thu Jul  2 06:49:44 2015  SHIBATA Hiroshi  <hsbt@ruby-lang.org>
 
 	* lib/rubygems: Update to RubyGems HEAD(c202db2).

lib/rubygems/resolver.rb

@@ -172,7 +172,7 @@ class Gem::Resolver
   include Molinillo::UI
 
   def output
-    @output ||= debug? ? $stdout : File.open('/dev/null', 'w')
+    @output ||= debug? ? $stdout : File.open(Gem::Util::NULL_DEVICE, 'w')
   end
 
   def debug?