Fix specification of Dawn Mac x64 DEPS Builder.

Builder's name in job was incorrect, so it wasn't getting scheduled.

Bug: 948902
Change-Id: I8731c706a77514f2b4d5e6e592d93a777ce113ef
Tbr: martiniss@chromium.org
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1562614Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649656}

infra/config/luci-scheduler.cfg

@@ -2066,7 +2066,7 @@ job {
   buildbucket: {
     server: "cr-buildbucket.appspot.com"
     bucket: "luci.chromium.ci"
-    builder: "Dawn Mac x64 Builder"
+    builder: "Dawn Mac x64 DEPS Builder"
   }
 }