html/template: fix doc typo

Fixes #4950.

R=golang-dev, peter
CC=golang-dev
https://golang.org/cl/7415046

src/pkg/html/template/doc.go

@@ -119,7 +119,7 @@ If {{.}} is the innocuous word, `left`, then it can appear more widely,
 Non-string values can be used in JavaScript contexts.
 If {{.}} is
 
-  []struct{A,B string}{ "foo", "bar" }
+  struct{A,B string}{ "foo", "bar" }
 
 in the escaped template