Update docs.voltha.org release version matrix.

howot/release/repositories/
  o Document more caveats for releasing indivdiual repositories.
  o repo:ci-management must be released twice:
    - first to establish a branhc for pipeline jobs.
    - second to update dependent versions after downstream repos have been released

Change-Id: I33d7f2442a1d4ea45a48caef0e49df92988cc2ce
diff --git a/VERSION b/VERSION
index 03aa22f..b221cd1 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.12.25
+2.12.26