content/methods.article: fix typo

Fixes golang/go#10667.

Change-Id: Ib6a61d6865f64abe8a659ee2087d30cdc1835401
Reviewed-on: https://go-review.googlesource.com/9671
Reviewed-by: Andrew Gerrand <adg@golang.org>
diff --git a/content/methods.article b/content/methods.article
index a5881bb..dff7d3a 100644
--- a/content/methods.article
+++ b/content/methods.article
@@ -87,7 +87,7 @@
 
 Go programs express error state with `error` values. 
 
-The `error` type is a built-in interface simliar to `fmt.Stringer`:
+The `error` type is a built-in interface similar to `fmt.Stringer`:
 
 	type error interface {
 		Error() string