Bug 1421062: Add nightly beetmover worker configuration; r=me

taskcluster/ci/config.yml

@@ -35,5 +35,7 @@ scriptworker:
             - 'project:comm:thunderbird:releng:signing:cert:release-signing'
         'scriptworker-prov-v1/tb-beetmover-dev':
             - 'project:comm:thunderbird:releng:beetmover:bucket:dep'
+        'scriptworker-prov-v1/tb-beetmover':
+            - 'project:comm:thunderbird:releng:beetmover:bucket:nightly'
         'scriptworker-prov-v1/tb-balrog-dev':
             - 'project:comm:thunderbird:releng:balrog:server:dep'