trace: fix EventLog example
trace: fix EventLog example

Fixes golang/go#12387

Change-Id: Iecc42d9f809bed10036d1c3af8838c2fbf7ea93d
Reviewed-on: https://go-review.googlesource.com/14014
Reviewed-by: David Symonds <7f6bb564ed9e580d4f0aa90d53b34578e5d24cb9@golang.org>

raboof/net,gomini/net,mckinney-subgraph/net,golang/net,albertjin/golang-net,gomini/net,veliamsli/net,flowlo/go-net,cmars/tools,cesanta/goxnet,veliamsli/net,DramaFever/golang.org-x-net,w4ngyi/net,cmars/tools,mckinney-subgraph/net,cmars/tools,flowlo/go-net,DramaFever/golang.org-x-net,w4ngyi/net,raboof/net,cesanta/goxnet,cmars/tools,albertjin/golang-net