Update kurbo and svg dependencies, fix a clippy warning. #1517

Job	Run time
cargo fmt	13s
cargo clippy+test (wasm32) (macOS-11)	2m 26s
cargo clippy+test (macOS-11)	51s
cargo clippy+test (windows-2019)	1m 27s
Docs (macOS-11)	3m 24s
cargo clippy+test (ubuntu-latest)	2m 46s
Docs (windows-2019)	3m 5s
cargo clippy+test (wasm32) (windows-2019)	3m 8s
Docs (ubuntu-latest)	1m 41s
cargo clippy+test (wasm32) (ubuntu-latest)	1m 11s
cargo test nightly (macOS-11)	1m 32s
cargo test nightly (windows-2019)	2m 13s
cargo test nightly (ubuntu-latest)	1m 56s
	25m 53s

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