[buildbucket] specify swarming hostname

it is required now

TBR=dpranke@chromium.org

Bug:
No-Try: true
No-Presubmit: true
Change-Id: I66b9796cc0cc5abfe4e93f9a5aa5e8101e3478b1
Reviewed-on: https://chromium-review.googlesource.com/812105
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
diff --git a/cr-buildbucket.cfg b/cr-buildbucket.cfg
index 265e7fa..eee7ee1 100644
--- a/cr-buildbucket.cfg
+++ b/cr-buildbucket.cfg
@@ -21,6 +21,7 @@
     group: "service-account-cq"
   }
   swarming {
+    hostname: "chromium-swarm.appspot.com"
     builder_defaults {
       dimensions: "pool:Chrome.LUCI"
       recipe {
@@ -55,6 +56,7 @@
     identity: "luci-scheduler@appspot.gserviceaccount.com"
   }
   swarming {
+    hostname: "chromium-swarm.appspot.com"
     builder_defaults {
       dimensions: "pool:Chrome.LUCI"
       recipe {