Update kurbo and svg dependencies, fix a clippy warning. #1516

Job	Run time
cargo fmt	13s
cargo test nightly (macOS-11)	1m 31s
cargo clippy+test (macOS-11)	53s
cargo test nightly (windows-2019)	2m 2s
Docs (macOS-11)	2m 59s
cargo clippy+test (windows-2019)	1m 20s
cargo test nightly (ubuntu-latest)	1m 45s
Docs (windows-2019)	3m 0s
cargo clippy+test (wasm32) (macOS-11)	2m 27s
cargo clippy+test (ubuntu-latest)	2m 39s
Docs (ubuntu-latest)	1m 44s
cargo clippy+test (wasm32) (windows-2019)	4m 42s
cargo clippy+test (wasm32) (ubuntu-latest)	1m 30s
	26m 45s

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