Bump version to 1.2.1-dev

Change-Id: If2872650111920f1dd3f4151971b022f0d2d6323
diff --git a/VERSION b/VERSION
index 26aaba0..538ee20 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.2.0
+1.2.1-dev