Don't omit test_parse_error_snippet on TruffleRuby

Author: byroot

test/json/json_parser_test.rb

@@ -862,7 +862,7 @@ def test_parse_error_incomplete_hash
   end
 
   def test_parse_error_snippet
-    omit "JRuby errors don't contain positions" unless RUBY_ENGINE == "ruby"
+    omit "JRuby errors don't contain positions" if RUBY_ENGINE == "jruby"
 
     error = assert_raise(JSON::ParserError) { JSON.parse("あああああああああああああああああああああああ") }
     assert_equal "unexpected character: 'ああああああああああ' at line 1 column 1", error.message