Bug 1274611: spell target-tasks.json with `-`; r=wcosta

MozReview-Commit-ID: Aij7wL3onop

--HG--
extra : rebase_source : a22fe4849b8494bf2bc460e2f7ce9be08f76ec69

taskcluster/taskgraph/decision.py

@@ -69,7 +69,7 @@ def taskgraph_decision(options):
                    taskgraph_to_json(tgg.full_task_graph))
 
     # write out the target task set to allow reproducing this as input
-    write_artifact('target_tasks.json',
+    write_artifact('target-tasks.json',
                    tgg.target_task_set.tasks.keys())
 
     # write out the optimized task graph to describe what will actually happen,