content/static/doc: fix typo in tutorial

Fixes golang/go#44019

Change-Id: Ib7798cfbfac76cf0107738c93de7ea7948a117df
Reviewed-on: https://go-review.googlesource.com/c/website/+/288293
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Trust: Carlos Amedee <carlos@golang.org>
Trust: Dmitri Shuralyov <dmitshur@golang.org>

content/static/doc/tutorial/greetings-multiple-people.html

@@ -120,7 +120,7 @@ func randomFormat() string {
         received names (as a key) with a generated message (as a value). In Go,
         you initialize a map with the following syntax:
         <code>make(map[<em>key-type</em>]<em>value-type</em>)</code>. You have
-        the <code>Hello</code> function return this map to the caller.
+        the <code>Hellos</code> function return this map to the caller.
       </li>
       <li>
         Loop through the names your function received, checking that each has a