[gradle-plugin] Fix serialization test (#2171)

tools/kotlin-native-gradle-plugin/build.gradle

@@ -141,8 +141,8 @@ test {
             sourceSets.test.output +
             files(shadowJar.archivePath) +
             configurations.shadow
-    systemProperty("kotlin.version", buildKotlinVersion)
-    systemProperty("kotlin.repo", buildKotlinCompilerRepo)
+    systemProperty("kotlin.version", kotlinVersion)
+    systemProperty("kotlin.repo", kotlinCompilerRepo)
     if (project.hasProperty("konan.home")) {
         systemProperty("konan.home", project.property("konan.home"))
     } else {

tools/kotlin-native-gradle-plugin/src/test/kotlin/ExperimentalPluginTests.kt

@@ -853,6 +853,7 @@ class ExperimentalPluginTests {
                 jcenter()
                 maven { it.setUrl("http://kotlin.bintray.com/kotlin-eap") }
                 maven { it.setUrl("http://kotlin.bintray.com/kotlin-dev") }
+                maven { it.setUrl(MultiplatformSpecification.KOTLIN_REPO) }
             }
             evaluate()
             tasks.withType(KotlinNativeCompile::class.java).all {