Update mainClassName property

This is required to work with Gradle 9. The mainClassName property
was deprecated back in Gradle 8.

See https://docs.gradle.org/current/userguide/upgrading_version_7.html#javaapplication_api_cleanup

Author: kahgoh

build.gradle

@@ -8,7 +8,10 @@ plugins {
 
 group = "org.exercism"
 version = "1.0-SNAPSHOT"
-mainClassName = "analyzer.AnalyzerCli"
+
+application {
+    mainClass = "analyzer.AnalyzerCli"
+}
 
 repositories {
     mavenCentral()