SONAR-1869: Fix creation of attribute 'Plugin-ChildFirstClassLoader'

subprojects/sonar-update-center/sonar-packaging-maven-plugin/src/main/java/org/sonar/updatecenter/mavenplugin/SonarPluginMojo.java

@@ -182,7 +182,7 @@ public class SonarPluginMojo extends AbstractSonarPluginMojo {
       getLog().info("-------------------------------------------------------");
 
       if (isUseChildFirstClassLoader()) {
-        archive.addManifestEntry(PluginManifest.USE_CHILD_FIRST_CLASSLOADER, true);
+        archive.addManifestEntry(PluginManifest.USE_CHILD_FIRST_CLASSLOADER, "true");
       }
 
       if (isSkipDependenciesPackaging()) {