[ruby/reline] Rename a temporary test name to appropriate one

https://github.com/ruby/reline/commit/26ebecde5c

test/reline/test_key_stroke.rb

@@ -36,7 +36,7 @@ class Reline::KeyStroke::Test < Reline::TestCase
     assert_equal(:matched, stroke.match_status("abzwabk".bytes))
   end
 
-  def test_aaa
+  def test_expand
     config = Reline::Config.new
     {
       'abc' => '123',