[gnome-nightly-oci] Use flatpak-builder:base image instead of the freedesktop 1.6 one.

[Jordan Petridis <jpetridis src gnome org>]

commit 098c5e44c13e66d3a5828c4b97e7576c28abe2ce
Author: Jordan Petridis <jordanpetridis protonmail com>
Date:   Fri May 18 12:31:19 2018 +0000

    Use flatpak-builder:base image instead of the freedesktop 1.6 one.

 gnome-master.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/gnome-master.yml b/gnome-master.yml
index 81859df..e4b7fd2 100644
--- a/gnome-master.yml
+++ b/gnome-master.yml
@@ -1,4 +1,4 @@
-FROM flatpak/flatpak-builder:freedesktop-1-6
+FROM flatpak/flatpak-builder:base
 
 RUN dnf install -y git xorg-x11-server-Xvfb && dnf clean all