Update patch version for release

New version is v1.2.1-dev

Bug:
Change-Id: I7d7abce62a53cffa0d64caf1626520a7b6ce8820
diff --git a/src/main/java/com/android/tools/r8/Version.java b/src/main/java/com/android/tools/r8/Version.java
index e51c08a..7d1fd9f 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 = "v1.2.0-dev";
+  public static final String LABEL = "v1.2.1-dev";
 
   private Version() {
   }