[gbm-web] Switch back to 18.04 due to apt dependency issues

[Bartłomiej Piotrowski <bpiotrowski src gnome org>]

commit 71df84bfbf940d895ade9c9ed85537b367eb437b
Author: Bartłomiej Piotrowski <bpiotrowski gnome org>
Date:   Wed Sep 16 12:17:59 2020 +0200

    Switch back to 18.04 due to apt dependency issues

 flat-manager/Dockerfile                         | 4 ++--
 flat-manager/Dockerfile.builder                 | 2 +-
 flat-manager/ppa_alexlarsson_flatpak.list       | 1 +
 flat-manager/ppa_alexlarsson_flatpak_focal.list | 1 -
 4 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/flat-manager/Dockerfile b/flat-manager/Dockerfile
index e084e8b..6348721 100644
--- a/flat-manager/Dockerfile
+++ b/flat-manager/Dockerfile
@@ -1,7 +1,7 @@
-FROM ubuntu:20.04
+FROM ubuntu:18.04
 
 RUN apt-get update && apt-get install -y gnupg2
-ADD ppa_alexlarsson_flatpak_focal.list /etc/apt/sources.list.d/
+ADD ppa_alexlarsson_flatpak.list /etc/apt/sources.list.d/
 RUN apt-key adv --keyserver keyserver.ubuntu.com --recv-keys C793BFA2FA577F07 && \
     apt-get update && apt-get install -y flatpak ostree libpq5 ca-certificates && \
     rm -rf /var/lib/apt/lists/*
diff --git a/flat-manager/Dockerfile.builder b/flat-manager/Dockerfile.builder
index 695fa5b..d991ed4 100644
--- a/flat-manager/Dockerfile.builder
+++ b/flat-manager/Dockerfile.builder
@@ -1,4 +1,4 @@
-FROM ubuntu:20.04
+FROM ubuntu:18.04
 
 RUN apt-get update && apt-get install -y git libpq-dev curl build-essential libgpgme-dev
 RUN curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs > rustup.sh && \
diff --git a/flat-manager/ppa_alexlarsson_flatpak.list b/flat-manager/ppa_alexlarsson_flatpak.list
new file mode 100644
index 0000000..d10254b
--- /dev/null
+++ b/flat-manager/ppa_alexlarsson_flatpak.list
@@ -0,0 +1 @@
+deb http://ppa.launchpad.net/alexlarsson/flatpak/ubuntu bionic main