Fix reference to "coarsened moment" (#473)

This fixes the following Biikeshed error:

    LINK ERROR: No 'dfn' refs found for 'coarsened moment' with for='['moment']'.
    [=moment/coarsened moment=]

"Coarsened moment" is a standalone definition. I probably meant to use a '|'
character instead of '/' when I wrote the original version, but just using
"coarsened moment" also works so use the latter.

index.bs

@@ -1435,7 +1435,7 @@ to {{SensorErrorEventInit}}.
     1.  Otherwise, [=map/set=] |reading|["timestamp"] to the [=unsafe shared current time=].
 
         Note: In neither case is an [=monotonic clock/unsafe current time=] ever exposed to script.
-        {{Sensor/timestamp|Sensor.timestamp}} always returns a [=moment/coarsened moment=] relative
+        {{Sensor/timestamp|Sensor.timestamp}} always returns a [=coarsened moment=] relative
         to a [=time origin=].
     1.  [=map/For each=] |key| → <var ignore>value</var> of [=latest reading=].
         1.  [=map/Set=] [=latest reading=][|key|] to the corresponding