doc/articles/wiki: use correct variable name in closures guide

Fixes non-existent variable TitleValidator to be validPath in
the closures, functions literal section.

Fixes #36779

Change-Id: I59762c358c3e00d1cc03d9d1e2aace03f145321d
GitHub-Last-Rev: a5e9b17
GitHub-Pull-Request: #36783
Reviewed-on: https://go-review.googlesource.com/c/go/+/216479
Reviewed-by: Emmanuel Odeke <[email protected]>

Author: howjmay

doc/articles/wiki/index.html

@@ -674,7 +674,7 @@ <h2>Introducing Function Literals and Closures</h2>
 an <code>http.ResponseWriter</code> and <code>http.Request</code> (in other
 words, an <code>http.HandlerFunc</code>).
 The closure extracts the <code>title</code> from the request path, and
-validates it with the <code>TitleValidator</code> regexp. If the
+validates it with the <code>validPath</code> regexp. If the
 <code>title</code> is invalid, an error will be written to the
 <code>ResponseWriter</code> using the <code>http.NotFound</code> function.
 If the <code>title</code> is valid, the enclosed handler function