doc: fix XML closing tag typo in network example

The example XML snippet has `<configuration>` as a closing tag instead of `</configuration>` - is should start with `</` as it's the end tag.

When the example is copied into a POM, the created POM is invalid.

src/site/apt/examples/deploy-network-issues.apt

@@ -48,7 +48,7 @@ Deploying With Network Issues
         <artifactId>maven-deploy-plugin</artifactId>
         <configuration>
           <retryFailedDeploymentCount>3</retryFailedDeploymentCount>
-        <configuration>
+        </configuration>
       </plugin>
     </plugins>
   </build>