trace: add missing td tag

Change-Id: I4f99953e028a6e397c62605f39b73872abf960bd
Reviewed-on: https://go-review.googlesource.com/c/net/+/670995
Reviewed-by: Sean Liao <sean@liao.dev>
Auto-Submit: Sean Liao <sean@liao.dev>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

trace/events.go

@@ -508,7 +508,7 @@ const eventsHTML = `
 	<tr class="first">
 		<td class="when">{{$el.When}}</td>
 		<td class="elapsed">{{$el.ElapsedTime}}</td>
-		<td>{{$el.Title}}
+		<td>{{$el.Title}}</td>
 	</tr>
 	{{if $.Expanded}}
 	<tr>