[gnome-builder] Update link to nightly build

[Christian Hergert <chergert src gnome org>]

commit 282c345799658cb9d9c5998481b4d021908c618a
Author: Heather Ellsworth <hellsworth gnome org>
Date:   Thu Oct 3 23:14:58 2019 +0000

    Update link to nightly build

 doc/help/installation.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/doc/help/installation.rst b/doc/help/installation.rst
index c59b2fa90..3f4081f23 100644
--- a/doc/help/installation.rst
+++ b/doc/help/installation.rst
@@ -44,7 +44,7 @@ You can also use the command line to install Builder:
 
 .. code-block:: sh
 
-   $ flatpak install --user --from 
https://gitlab.gnome.org/GNOME/gnome-apps-nightly/raw/master/gnome-builder.flatpakref
+   $ flatpak install --user --from https://nightly.gnome.org/repo/appstream/org.gnome.Builder.flatpakref
    $ flatpak run org.gnome.Builder
 
 .. note:: Nightly builds are built with tracing enabled. The tracing is fairly lightweight, but it includes 
a great deal of more debugging information.