update book #254

Job	Run time
Intra-doc links	1m 23s
Build target wasm32-unknown-unknown	1m 46s
Bitrot check	1m 46s
Book tests	1m 19s
Build target wasm32-wasi	1m 34s
Rustfmt	19s
Test on ubuntu-latest	7m 9s
Test on windows-latest	11m 17s
Test on i686-unknown-linux-gnu	13m 15s
Test on macOS-latest	7m 23s
Test on i686-unknown-linux-gnu with beta features	13m 23s
Test on ubuntu-latest with beta features	7m 10s
Test on i686-unknown-linux-gnu with nightly features	15m 32s
Test on windows-latest with beta features	9m 59s
Test on macOS-latest with beta features	6m 31s
Test on ubuntu-latest with nightly features	8m 8s
Test on windows-latest with nightly features	11m 51s
Test on macOS-latest with nightly features	10m 10s
	2h 9m 55s

Provide feedback