docker: Fix debian channel to stable

Currently there is no "testing" directory in:

http://osm-download.etsi.org/repository/osm/debian/ReleaseFIVE/dists/

Change-Id: Ib43722865573a7ec386082bd1af4375af26db108
Signed-off-by: Philippe Coval <rzr@users.sf.net>
diff --git a/Dockerfile.fromdeb b/Dockerfile.fromdeb
index f9b0a6d..9c3e245 100644
--- a/Dockerfile.fromdeb
+++ b/Dockerfile.fromdeb
@@ -18,7 +18,7 @@
 ARG REPOSITORY_BASE=http://osm-download.etsi.org/repository/osm/debian
 ARG RELEASE=ReleaseFIVE
 ARG REPOSITORY_KEY=OSM%20ETSI%20Release%20Key.gpg
-ARG REPOSITORY=testing
+ARG REPOSITORY=stable
 
 RUN apt-get update && apt-get install -y curl software-properties-common
 RUN curl ${REPOSITORY_BASE}/${RELEASE}/${REPOSITORY_KEY} | apt-key add -