Jenkinsfile: Fix deploy step.

A variable had not been renamed properly, causing an unbound variable
exception to be thrown.

* Jenkinsfile ('Sign & deploy packages') <target>: Rename variable to ...
<distribution> in the later loop.

Change-Id: I6c92b3249b537a91cec58438bfbcf8780043d74e

Jenkinsfile

@@ -204,7 +204,7 @@ See https://wiki.savoirfairelinux.com/wiki/Jenkins.jami.net#Configuration_client
                     distributions.each { distribution ->
                         echo "Deploying ${distribution} packages..."
                         sh """scripts/deploy-packages.sh \
-  --distribution=${target} \
+  --distribution=${distribution} \
   --keyid="${RING_PUBLIC_KEY_FINGERPRINT}" \
   --snapcraft-login="${SNAPCRAFT_KEY}" \
   --remote-ssh-identity-file="${SSH_PRIVATE_KEY}" \