Doc: add a space #2724

Job	Run time
Build (nightly, bench,serde,bt,singlethreaded)	1m 14s
openraft-test-bench (nightly)	54s
cluster-benchmark (cluster_benchmark)	47s
examples (stable, raft-kv-memstore)	2m 50s
examples (stable, raft-kv-rocksdb)	8m 6s
external-stores (stores/rocksstore-v2)	5m 54s
lint	6m 32s
examples (nightly, raft-kv-memstore)	3m 59s
openraft-feature-test (nightly)	57s
examples (nightly, raft-kv-rocksdb)	12m 0s
openraft-test (stable, 0)	2m 58s
openraft-feature-test (nightly, serde)	47s
openraft-test (nightly, 30)	3m 15s
openraft-feature-test (nightly, single-term-leader)	1m 19s
openraft-test (nightly, 0, single-term-leader)	2m 54s
stores (memstore)	57s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	49s
stores (rocksstore)	6m 0s
stores (rocksstore-compat07)	6m 6s
tests-feature-test (nightly)	2m 39s
stores (sledstore)	1m 21s
tests-feature-test (nightly, single-term-leader)	2m 43s
tests-feature-test (nightly, loosen-follower-log-revert)	2m 45s
	1h 17m 46s

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