Fix updating the mapping file with additional comment

Change-Id: I78dadbed9e199dcda2d4c088e1d08474098a2620
diff --git a/src/main/java/com/android/tools/r8/naming/ProguardMapSupplier.java b/src/main/java/com/android/tools/r8/naming/ProguardMapSupplier.java
index 20704a5..011a7ba 100644
--- a/src/main/java/com/android/tools/r8/naming/ProguardMapSupplier.java
+++ b/src/main/java/com/android/tools/r8/naming/ProguardMapSupplier.java
@@ -97,7 +97,7 @@
     }
     builder.append("# " + MARKER_KEY_PG_MAP_ID + ": " + proguardMapId + "\n");
     // Turn off linting of the mapping file in some build systems.
-    builder.append("# common_typos_disable");
+    builder.append("# common_typos_disable" + "\n");
     builder.append(body);
 
     return new ProguardMapAndId(builder.toString(), proguardMapId);