Gradle, JS: fix TCServiceMessageOutputStreamHandlerTest on windows

libraries/tools/kotlin-gradle-plugin/src/test/kotlin/org/jetbrains/kotlin/gradle/internal/testing/TCServiceMessageOutputStreamHandlerTest.kt

@@ -171,15 +171,15 @@ class TCServiceMessageOutputStreamHandlerTest {
         val log = StringBuffer()
 
         override fun parseException(p0: ParseException, p1: String) {
-            log.appendln("EXCEPTION `$p0`, `$p1`")
+            log.append("EXCEPTION `$p0`, `$p1`\n")
         }
 
         override fun serviceMessage(p0: ServiceMessage) {
-            log.appendln("MESSAGE: `$p0`")
+            log.append("MESSAGE: `$p0`\n")
         }
 
         override fun regularText(p0: String) {
-            log.appendln("TEXT: `$p0`")
+            log.append("TEXT: `$p0`\n")
         }
     }
 }