[retro-gtk] hacking: Add the hyphen to the issue URLs

[Adrien Plazas <aplazas src gnome org>]

commit 72c67f97fd6f59dc9712d4bdf09422e8c4c6eaf9
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Wed Oct 14 08:23:16 2020 +0200

    hacking: Add the hyphen to the issue URLs

 HACKING.md | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/HACKING.md b/HACKING.md
index b9e0f5cd..d46f1050 100644
--- a/HACKING.md
+++ b/HACKING.md
@@ -11,7 +11,7 @@ any external or private interfaces changed, what bugs were fixed (with
 bug tracker reference if applicable) and so forth. Be concise but not
 too brief.
 
-Fixes https://gitlab.gnome.org/GNOME/retro-gtk/issues/1.
+Fixes https://gitlab.gnome.org/GNOME/retro-gtk/-/issues/1.
 ```
 
 ### The Tag
@@ -105,12 +105,12 @@ Do not simply use the issue number.
 
 Good issue references:
 ```
-Fixes https://gitlab.gnome.org/GNOME/retro-gtk/issues/1.
+Fixes https://gitlab.gnome.org/GNOME/retro-gtk/-/issues/1.
 ```
 
 Bad issue references:
 ```
 Fixes #1
-Fix https://gitlab.gnome.org/GNOME/retro-gtk/issues/1.
-Fixes https://gitlab.gnome.org/GNOME/retro-gtk/issues/1
+Fix https://gitlab.gnome.org/GNOME/retro-gtk/-/issues/1.
+Fixes https://gitlab.gnome.org/GNOME/retro-gtk/-/issues/1
 ```