net: fix typo in dns client unix test

Fix a typo DNS name, it should be [onion.vegetables.com](http://onion.vegetables.com/)

Change-Id: I4122a2305b8f5e774a834651e70c75b54e9386bd
GitHub-Last-Rev: 9907897944275c5f8c54c79667cbb1ef474539de
GitHub-Pull-Request: golang/go#36270
Reviewed-on: https://go-review.googlesource.com/c/go/+/212410Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/net/dnsclient_unix_test.go

@@ -173,7 +173,7 @@ func TestAvoidDNSName(t *testing.T) {
 
 		// Without stuff before onion/local, they're fine to
 		// use DNS. With a search path,
-		// "onion.vegegtables.com" can use DNS. Without a
+		// "onion.vegetables.com" can use DNS. Without a
 		// search path (or with a trailing dot), the queries
 		// are just kinda useless, but don't reveal anything
 		// private.