Fix clippy warnings #545

Job	Run time
Bitrot check	1m 23s
Book tests	1m 48s
Code coverage	3h 2m 52s
Build target wasm32-unknown-unknown	2m 10s
Intra-doc links	1m 53s
Build target wasm32-wasi	1m 59s
Rustfmt	12s
Test on ubuntu-latest	10m 47s
Test on i686-unknown-linux-gnu	23m 10s
Test on windows-latest	14m 19s
Test on i686-unknown-linux-gnu with beta features	23m 7s
Test on i686-unknown-linux-gnu with nightly features	22m 7s
Test on macOS-latest	9m 10s
Test on ubuntu-latest with beta features	11m 6s
Test on windows-latest with beta features	14m 8s
Test on macOS-latest with beta features	12m 17s
Test on ubuntu-latest with nightly features	11m 7s
Test on windows-latest with nightly features	14m 28s
Test on macOS-latest with nightly features	10m 42s
	6h 8m 45s

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