Fix loading of config file with recent Rubies (Psych 4.0)

Using Ruby 3.2, the following command would fail like this without the fix:

    > bin\kramdown --config-file .kramdown.yml -i GFM -o html README.md
    .../ruby-3.2-lean/lib/ruby/3.2.0/psych.rb:322:in `safe_load': wrong number of arguments (given 2, expected 1) (ArgumentError)
        from .../vendor/ruby/3.2.0/gems/kramdown-2.4.0/bin/kramdown:114:in `<top (required)>'
        from .../bin/kramdown.cmd:30:in `load'
        from .../bin/kramdown.cmd:30:in `<main>'

bin/kramdown

@@ -111,7 +111,12 @@ end.parse!
 
 begin
   if config_file && File.exist?(config_file)
-    config_file_options = YAML.safe_load(File.read(config_file), [Symbol])
+    config_file_options =
+      if YAML.method(:safe_load).parameters.include?(%i[key permitted_classes])
+        YAML.safe_load(File.read(config_file), permitted_classes: [Symbol])
+      else # compatibility with Psych < 3.1.0
+        YAML.safe_load(File.read(config_file), [Symbol])
+      end
     case config_file_options
     when nil # empty configuration file except perhaps YAML header and comments
       # Nothing to do