Fix typo.

reported by Nobuhiro IMAI.$
https://twitter.com/no6v/status/176959588531314688

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@34931 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_sleep.rb

@@ -6,7 +6,7 @@ class TestSleep < Test::Unit::TestCase
     start = Time.now
     sleep 5
     slept = Time.now-start
-    bottom = /linux/ =~ RUBY_PLATFORM && /Linux ([\d.]+)/ =~ `uname -sr` && ($1.split('.')<=>%w/2 6.18/)<1 ? 4.99 : 5.0
+    bottom = /linux/ =~ RUBY_PLATFORM && /Linux ([\d.]+)/ =~ `uname -sr` && ($1.split('.')<=>%w/2 6 18/)<1 ? 4.99 : 5.0
     assert_operator(bottom, :<=, slept)
     assert_operator(slept, :<=, 6.0, "[ruby-core:18015]: longer than expected")
   ensure