Bump VERSION string to release, see if this will publish to https://docs.voltha.org

Change-Id: I6e4de2d27a6a68d94b0690250e99d7e397ce9844
diff --git a/VERSION b/VERSION
index 7eeb432..e464374 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.12.5.5-dev
+2.12.6