[ruby/rdoc] Fix an exception class name

https://github.com/ruby/rdoc/commit/87301da71b

lib/rdoc/known_classes.rb

@@ -36,7 +36,7 @@ module RDoc
     "rb_cTime"             => "Time",
     "rb_cTrueClass"        => "TrueClass",
 
-    "rb_eArgError"         => "ArgError",
+    "rb_eArgError"         => "ArgumentError",
     "rb_eEOFError"         => "EOFError",
     "rb_eException"        => "Exception",
     "rb_eFatal"            => "fatal",

test/rdoc/test_rdoc_parser_c.rb

@@ -115,6 +115,8 @@ class TestRDocParserC < RDoc::TestCase
 
     parser = RDoc::Parser::C.new @top_level, @fn, '', @options, @stats
 
+    assert_equal "ArgumentError", parser.known_classes["rb_eArgError"]
+
     expected = { 'cSomeExt' => some_ext }
     assert_equal expected, parser.classes