Update patch version for release - new version is 1.5.20-dev

Change-Id: Ic6f3b25eee760c1e05111d9543bb5f5aeafa154f
diff --git a/src/main/java/com/android/tools/r8/Version.java b/src/main/java/com/android/tools/r8/Version.java
index ade7991..588967b 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 = "1.5.19-dev";
+  public static final String LABEL = "1.5.20-dev";
 
   private Version() {
   }