build(deps): update yew requirement from 0.20 to 0.21

Updates the requirements on [yew](https://github.com/yewstack/yew) to permit the latest version.
- [Release notes](https://github.com/yewstack/yew/releases)
- [Changelog](https://github.com/yewstack/yew/blob/master/CHANGELOG.md)
- [Commits](yewstack/yew@yew-v0.20.0...yew-v0.21.0)

---
updated-dependencies:
- dependency-name: yew
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

examples/wasm/Cargo.toml

@@ -13,4 +13,4 @@ qrcode-generator = "4"
 ur = { path = "../.." }
 wasm-bindgen = "0.2"
 web-sys = { version = "0.3", features = ["Event","EventTarget","InputEvent"] }
-yew = { version = "0.20", features = ["csr"] }
+yew = { version = "0.21", features = ["csr"] }