`defaultPathSerializer` doesn't url-encode its primitive string params

[maslennikov]

Description

After upgrade from v0.8.2 to v0.9.3 I noticed breaking behavior. When passing raw strings as path params, they don't get url-encoded.

Reproduction

console.log(defaultPathSerializer('/hello/{slug}', {slug: '/foo?bar'}))
// output: /hello//foo?bar

Expected result

"/hello/%2Ffoo%3Fbar"

Checklist

• [ ] I’m willing to open a PR (see CONTRIBUTING.md)