update to 1.2.1-pre2 in BUILD file too
diff --git a/BUILD b/BUILD
index db08f57..faaef51 100644
--- a/BUILD
+++ b/BUILD
@@ -41,7 +41,7 @@
 
 core_version = "3.0.0-dev"
 
-version = "1.2.0"
+version = "1.2.1-pre2"
 
 grpc_cc_library(
     name = "gpr",