Bump VERSION to v1.12.1-rc2

Signed-off-by: Tibor Vass <tibor@docker.com>
diff --git a/VERSION b/VERSION
index e8e560f..c2cbf3e 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.12.1-rc1
+1.12.1-rc2