test_time.rb: use UTC

* test/ruby/test_time.rb (test_strftime_no_hidden_garbage): fix
  failure due to timezone offset.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57494 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_time.rb

@@ -1092,7 +1092,7 @@ class TestTime < Test::Unit::TestCase
 
   def test_strftime_no_hidden_garbage
     fmt = %w(Y m d).map { |x| "%#{x}" }.join('-') # defeats optimization
-    t = Time.at(0)
+    t = Time.at(0).getutc
     ObjectSpace.count_objects(res = {}) # creates strings on first call
     before = ObjectSpace.count_objects(res)[:T_STRING]
     val = t.strftime(fmt)