[x/tour] content/methods.article: fix typo
[x/tour] content/methods.article: fix typo

Fixes golang/go#10667.

Change-Id: Ib6a61d6865f64abe8a659ee2087d30cdc1835401
Reviewed-on: https://go-review.googlesource.com/9671
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>
X-Tour-Commit: 6118f58319e877fd189196234d8ebf286bf8d47e

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website