content: use uniform dashes in translation links

Fixes golang/tour#1179

Change-Id: I080c12cad0a6a6d2e4bee9b5af1aa01cb90e4a5a
Reviewed-on: https://go-review.googlesource.com/c/tour/+/319309
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

content/welcome.article

diff --git a/content/welcome.article b/content/welcome.article
index bca274e..e96256a 100644
--- a/content/welcome.article
+++ b/content/welcome.article
@@ -55,8 +55,8 @@
 - [[https://go-tour-id2.appspot.com/][Indonesian — Bahasa Indonesia]]
 - [[https://go-tour-jp.appspot.com/][Japanese — 日本語]]
 - [[https://go-tour-ko.appspot.com/][Korean — 한국어]]
-- [[https://go-tour-pl1.appspot.com/][Polish - Polski]]
-- [[https://go-tour-th.appspot.com/][Thai - ภาษาไทย]]
+- [[https://go-tour-pl1.appspot.com/][Polish — Polski]]
+- [[https://go-tour-th.appspot.com/][Thai — ภาษาไทย]]
 - [[https://go-tour-uz.appspot.com/][Uzbek — Ўзбекча]]
 
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