Fix RocketMQ Document Typesetting Errors

[zhibo6]

Fix RocketMQ Document Typesetting Errors

What is the purpose of the change

文档排版纠错

Brief changelog

"##3 消息过滤" 改为 "## 3 消息过滤"

Verifying this change

无需验证

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[coveralls]

Coverage increased (+0.05%) to 50.625% when pulling 3cd6a4a on zhibo6:patch-2 into 15df329 on apache:master.