Fix wrong closing tag

Fixes gh-874

spring-boot-tools/spring-boot-maven-plugin/src/site/apt/usage.apt.vm

@@ -123,7 +123,7 @@ mvn spring-boot:run
       <artifactId>${project.artifactId}</artifactId>
       <version>${project.version}</version>
       <configuration>
-        <addResources>false</mainClass>
+        <addResources>false</addResources>
       </configuration>
     </plugin>
     ...