content: update location of Turkish translation

Update golang-tr/go-tour-tr#2

Change-Id: I9e360f3a07a26432d671ce5872c9eb9e15a84375
Reviewed-on: https://go-review.googlesource.com/23334
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/content/welcome.article b/content/welcome.article
index 0560410..a121688 100644
--- a/content/welcome.article
+++ b/content/welcome.article
@@ -62,7 +62,7 @@
 - [[https://go-tour-zh-tw.appspot.com/][Traditional Chinese — 中文(繁體)]]
 - [[https://go-tour-ua.appspot.com/][Ukrainian — Українська]]
 - [[https://go-tour-uz.appspot.com/][Uzbek — Ўзбекча]]
-- [[http://tur.a.golang.org.tr/][Turkish - Türkçe]]
+- [[https://go-tour-turkish.appspot.com/][Turkish - Türkçe]]
 
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