docs(examples): touch up Hello server example #2404

Job	Run time
Verify hyper.h is up to date	26s
Check Style	14s
Test C API (FFI)	24s
Test with Miri	2m 40s
minimal-versions	35s
features	18s
Check MSRV	26s
udeps	27s
Test stable on ubuntu-latest	1m 14s
Test stable on windows-latest	1m 50s
Test stable on macOS-latest	1m 32s
Test beta on ubuntu-latest	1m 6s
Test beta on windows-latest	1m 52s
Test beta on macOS-latest	1m 26s
Test nightly on ubuntu-latest	1m 34s
Test nightly on windows-latest	2m 25s
Test nightly on macOS-latest	2m 49s
Build docs	29s
Check exposed types	16s
CI is green	1s
	22m 4s

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