reduce errors #275

Job	Run time
Bitrot check	1m 12s
Book tests	1m 36s
Build target wasm32-unknown-unknown	2m 0s
Build target wasm32-wasi	1m 55s
Code coverage	21m 23s
Intra-doc links	1m 49s
Rustfmt	15s
Test on ubuntu-latest	3m 32s
Test on i686-unknown-linux-gnu	3m 42s
Test on windows-latest	3m 33s
Test on macOS-latest	3m 29s
Test on ubuntu-latest with beta features	3m 33s
Test on windows-latest with beta features	3m 32s
Test on i686-unknown-linux-gnu with beta features	3m 42s
Test on macOS-latest with beta features	3m 29s
Test on i686-unknown-linux-gnu with nightly features	3m 43s
Test on ubuntu-latest with nightly features	3m 28s
Test on windows-latest with nightly features	3m 34s
Test on macOS-latest with nightly features	3m 34s
	1h 13m 1s

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