fix: Drop deprecated API usage

Author: osipxd

src/main/groovy/ru/endlesscode/bukkitgradle/task/PrepareServer.groovy

@@ -62,8 +62,8 @@ class PrepareServer extends DefaultTask {
     void copyPluginsToServerDir() {
         String pluginName = "${project.bukkit.meta.name}.jar"
         List<Path> paths = project.tasks.withType(Jar).collect { jar ->
-            if (jar.classifier in ["src", "source", "sources", "javadoc"]) return
-            jar.archivePath.toPath()
+            if (jar.archiveClassifier.get() in ["src", "source", "sources", "javadoc"]) return
+            jar.archiveFile.get().asFile.toPath()
         }
 
         Path pluginsDir = getServerDir().resolve("plugins")