Bug 1546801: [firefox-ci] Update default taskcluster; r=Callek a=tomprince CLOSED TREE

MANUAL PUSH: Initial push to test new firefox-ci taskcluster cluster.

Differential Revision: https://phabricator.services.mozilla.com/D52453

--HG--
extra : histedit_source : 4bcac76e95d5566db7bb892d44830c03a615f78f

taskcluster/taskgraph/util/taskcluster.py

@@ -24,7 +24,7 @@ testing = False
 
 # Default rootUrl to use if none is given in the environment; this should point
 # to the production Taskcluster deployment used for CI.
-PRODUCTION_TASKCLUSTER_ROOT_URL = 'https://taskcluster.net'
+PRODUCTION_TASKCLUSTER_ROOT_URL = 'https://firefox-ci-tc.services.mozilla.com'
 
 # the maximum number of parallel Taskcluster API calls to make
 CONCURRENCY = 50