update publishing

publish.gradle

@@ -3,6 +3,9 @@ apply plugin: 'maven-publish'
 task javadocsJar(type: Jar) {
     classifier = 'javadoc'
 }
+task sourceJar (type : Jar) {
+    classifier = 'sources'
+}
 
 afterEvaluate {
     project.publishing.publications.all {
@@ -10,6 +13,7 @@ afterEvaluate {
         groupId "${project.group}"
         if (it.name.contains('kotlinMultiplatform')) {
             artifactId = "${project.name}"
+            artifact sourceJar
         } else {
             artifactId = "${project.name}-$name"
         }