[gnome-runtime-images] base: use hypens for the remote name

[Jordan Petridis <jpetridis src gnome org>]

commit c6d73560d9f2e78e48adffbb903a4f87d5344c86
Author: Jordan Petridis <jpetridis gnome org>
Date:   Tue Sep 10 15:52:17 2019 +0300

    base: use hypens for the remote name

 base | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/base b/base
index 8ee8ea1..a95c290 100644
--- a/base
+++ b/base
@@ -11,7 +11,7 @@ RUN dnf -y update && \
 
 RUN flatpak remote-add flathub https://dl.flathub.org/repo/flathub.flatpakrepo && \
     flatpak remote-add gnome-nightly https://sdk.gnome.org/gnome-nightly.flatpakrepo && \
-    flatpak remote-add flathub_beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo
+    flatpak remote-add flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo
 
 # Add a machine-id as specified in the freedesktop spec:
 # https://www.freedesktop.org/software/systemd/man/machine-id.html