doc/articles/wiki: don't run tests when 'patch' command unavailable

Change-Id: I21cfea3eadb37904252900324c23e2664b121bbb
Reviewed-on: https://go-review.googlesource.com/11099
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

doc/articles/wiki/test.bash

@@ -4,6 +4,12 @@
 # license that can be found in the LICENSE file.
 
 set -e
+
+if ! which patch > /dev/null; then
+	echo "Skipping test; patch command not found."
+	exit 0
+fi
+
 wiki_pid=
 cleanup() {
 	kill $wiki_pid