Update patch version for release - new version is 1.3.9-dev

Bug: b/111537015
Change-Id: I396154a756c8a6d770fdc1e72e0b0462907e007e
diff --git a/src/main/java/com/android/tools/r8/Version.java b/src/main/java/com/android/tools/r8/Version.java
index 0990f79..4025180 100644
--- a/src/main/java/com/android/tools/r8/Version.java
+++ b/src/main/java/com/android/tools/r8/Version.java
@@ -11,7 +11,7 @@
 
   // This field is accessed from release scripts using simple pattern matching.
   // Therefore, changing this field could break our release scripts.
-  public static final String LABEL = "1.3.8-dev";
+  public static final String LABEL = "1.3.9-dev";
 
   private Version() {
   }