Merge pull request #833 from zcash/fix-ci #4072

Job	Run time
Bitrot check	1m 37s
Book tests	1m 25s
Code coverage	3m 29s
Build target wasm32-unknown-unknown	1m 49s
Intra-doc links	1m 27s
Build target wasm32-wasi	1m 40s
Rustfmt	17s
Test on ubuntu-latest	7m 16s
Test on windows-latest	10m 55s
Test on i686-unknown-linux-gnu	13m 50s
Test on macOS-latest	6m 26s
Test on i686-unknown-linux-gnu with beta features	13m 11s
Test on i686-unknown-linux-gnu with nightly features	15m 55s
Test on ubuntu-latest with beta features	7m 24s
Test on windows-latest with beta features	10m 53s
Test on macOS-latest with beta features	6m 26s
Test on ubuntu-latest with nightly features	8m 11s
Test on windows-latest with nightly features	11m 58s
Test on macOS-latest with nightly features	7m 14s
	2h 11m 23s

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