Fixes a type in the section markup of Reacting to the Maven plugin. This broke the AsciiDoc syntax with the following result in the HTML published version. Instead of a title and admonitions we get a paragraf with all together.

SpringBoot Fix typo in 'Reacting to the Maven plugin' title

Comment From: pivotal-cla

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Comment From: pivotal-cla

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Comment From: snicoll

Good catch, thank you!