Fix directory leak in test_cleanup

Library/Homebrew/test/test_cmd_cleanup.rb

@@ -23,5 +23,8 @@ class CleanupTests < Homebrew::TestCase
     refute_predicate f1, :installed?
     refute_predicate f2, :installed?
     assert_predicate f3, :installed?
+  ensure
+    [f1, f2, f3].each(&:clear_cache)
+    f3.rack.rmtree
   end
 end