Fix a test message.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54865 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/ruby/test_file_exhaustive.rb

@@ -184,7 +184,7 @@ class TestFileExhaustive < Test::Unit::TestCase
   end
 
   def assert_integer_or_nil(n)
-    msg = ->{"#{n.inspect} is neither Fixnum nor nil."}
+    msg = ->{"#{n.inspect} is neither Integer nor nil."}
     if n
       assert_kind_of(Integer, n, msg)
     else