chore(ci): fix rustfmt edition to 2018 #2281

Job	Run time
Check Style	16s
Verify hyper.h is up to date	20s
Test with Miri	1m 12s
features	21s
Test C API (FFI)	16s
Check MSRV	1m 15s
Test stable on ubuntu-latest	1m 55s
udeps	44s
Test stable on windows-latest	3m 57s
Test stable on macOS-latest	1m 23s
Test beta on ubuntu-latest	1m 12s
Test beta on windows-latest	2m 33s
Test beta on macOS-latest	1m 52s
Test nightly on ubuntu-latest	1m 17s
Test nightly on windows-latest	3m 48s
Test nightly on macOS-latest	2m 49s
Check exposed types	16s
Build docs	34s
CI is green	1s
	26m 1s

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