Add missing space on doc comment. #2024

Job	Run time
Clippy	55s
Docs	1m 21s
Examples Rust nightly	4m 20s
Examples Rust beta	3m 56s
Format	4s
Test forcing wrapper generation	7m 30s
Examples Rust stable	4m 33s
Outdated	9s
Examples macOS	3m 54s
Address Sanitizer	12m 9s
Examples Windows (gnu)	6m 8s
Test Rust nightly	8m 16s
Examples Windows (msvc)	4m 49s
Test Rust beta	9m 32s
Test Rust stable	10m 12s
Test macOS	10m 48s
Test Windows (msvc)	13m 8s
	1h 41m 44s

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