Fix a typo SetType => SetGoatType in example code

The metric name in the example is "GoatType", not "Type".

Change-Id: Ic6055c3b6ee095f319395e22108eb9d0e21f052d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2618781Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Wan-Teh Chang <wtc@google.com>
Cr-Commit-Position: refs/heads/master@{#842121}

services/metrics/ukm_api.md

@@ -238,7 +238,7 @@ void OnGoatTeleported() {
   ...
   ukm::builders::Goat_Teleported(source_id)
       .SetDuration(duration.InMilliseconds())
-      .SetType(goat_type)
+      .SetGoatType(goat_type)
       .Record(ukm_recorder);
 }
 ```