[Retrace] Always use \n as line separator for partitions

Change-Id: Icc3c2fa79d4bd5cd798d066eebd4af0b3215ec62
diff --git a/src/main/java/com/android/tools/r8/retrace/internal/ProguardMapPartitionerOnClassNameToText.java b/src/main/java/com/android/tools/r8/retrace/internal/ProguardMapPartitionerOnClassNameToText.java
index 7ef3d1c..9770a0b 100644
--- a/src/main/java/com/android/tools/r8/retrace/internal/ProguardMapPartitionerOnClassNameToText.java
+++ b/src/main/java/com/android/tools/r8/retrace/internal/ProguardMapPartitionerOnClassNameToText.java
@@ -68,7 +68,7 @@
     reader.forEachClassMapping(
         (classMapping, entries) -> {
           try {
-            String payload = StringUtils.joinLines(entries);
+            String payload = StringUtils.join("\n", entries);
             ClassNameMapper classNameMapper = ClassNameMapper.mapperFromString(payload);
             if (classNameMapper.getClassNameMappings().size() != 1) {
               diagnosticsHandler.error(