Fix tests to work with current FileUtils

Historically, FileUtils logged verbose output to stderr instead of
stdout.  This was fixed in FileUtils to log verbose output to
stdout (since it isn't an error).  This commit adjusts the tests to
handle both FileUtils versions.

test/test_rake_clean.rb

@@ -40,11 +40,20 @@ def test_cleanup_ignores_missing_files
   def test_cleanup_trace
     file_name = create_file
 
-    assert_output "", "rm -r #{file_name}\n" do
+    out, err = capture_io do
       with_trace true do
         Rake::Cleaner.cleanup(file_name)
       end
     end
+
+    if err == ""
+      # Current FileUtils
+      assert_equal "rm -r #{file_name}\n", out
+    else
+      # Old FileUtils
+      assert_equal "", out
+      assert_equal "rm -r #{file_name}\n", err
+    end
   end
 
   def test_cleanup_without_trace
@@ -70,11 +79,18 @@ def test_cleanup_opt_overrides_trace_silent
   def test_cleanup_opt_overrides_trace_verbose
     file_name = create_file
 
-    assert_output "", "rm -r #{file_name}\n" do
+    out, err = capture_io do
       with_trace false do
         Rake::Cleaner.cleanup(file_name, verbose: true)
       end
     end
+
+    if err == ""
+      assert_equal "rm -r #{file_name}\n", out
+    else
+      assert_equal "", out
+      assert_equal "rm -r #{file_name}\n", err
+    end
   end
 
   private