_content/doc/articles/wiki: update 'OS X' to 'macOS'

As macOS is now in version 11, or XI, which Go supports. There is no
need to specify OS X as a prerequisite now, it would be more correct
to specify just 'macOS'.

Change-Id: Ida07bb513e75c9700e77eb57278604e76d2afa24
GitHub-Last-Rev: 8a47eedc88e4953fab3da1e145aa5564a459416f
GitHub-Pull-Request: golang/website#50
Reviewed-on: https://go-review.googlesource.com/c/website/+/312712
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Heschi Kreinick <heschi@google.com>
diff --git a/_content/doc/articles/wiki/index.html b/_content/doc/articles/wiki/index.html
index a74a58e..b3e808b 100644
--- a/_content/doc/articles/wiki/index.html
+++ b/_content/doc/articles/wiki/index.html
@@ -28,7 +28,7 @@
 <h2>Getting Started</h2>
 
 <p>
-At present, you need to have a FreeBSD, Linux, OS X, or Windows machine to run Go.
+At present, you need to have a FreeBSD, Linux, macOS, or Windows machine to run Go.
 We will use <code>$</code> to represent the command prompt.
 </p>