fix github running error #248

Job	Run time
Book tests	1m 12s
Bitrot check	1m 38s
Build target wasm32-unknown-unknown	1m 40s
Build target wasm32-wasi	1m 28s
Intra-doc links	1m 18s
Rustfmt	13s
Test on ubuntu-latest	6m 58s
Test on i686-unknown-linux-gnu	12m 59s
Test on windows-latest	9m 53s
Test on i686-unknown-linux-gnu with beta features	13m 17s
Test on macOS-latest	6m 49s
Test on i686-unknown-linux-gnu with nightly features	14m 47s
Test on ubuntu-latest with beta features	7m 1s
Test on windows-latest with beta features	10m 20s
Test on macOS-latest with beta features	6m 40s
Test on ubuntu-latest with nightly features	8m 10s
Test on windows-latest with nightly features	11m 36s
Test on macOS-latest with nightly features	7m 14s
	2h 3m 13s

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