I'm not 100% sure what to do with this. Right now, calling `"#{0xe2.chr}#{0x80.chr}#{0xa8.chr}".to_json` (with or without ActiveSupport) causes "Encoding::UndefinedConversionError: "\xE2" from ASCII-8BIT to UTF-8". On 4-0-stable, it returns "\"���\"". I don't know if we actually care about this cause there are no test cases covering this.