Without this change, non-latin characters are not escaped and Ruby throws incompatible string encoding exception (US-ASCII v.s. UTF-8).

But with this change, some characters in `URI::PATTERN::RESERVED` are not escaped properly:

```irb
2.0.0-p451 :006 > URI.encode URI::PATTERN::RESERVED
 => ";/?:@&=+$,%5C[%5C]"
2.0.0-p451 :007 > URI.encode URI::PATTERN::RESERVED, URI::PATTERN::RESERVED
 => "%3B%2F%3F%3A%40%26%3D%2B%24%2C%5C%5B%5C%5D"
```