Add some debug commands to work around postgres issue in image

.appveyor.yml

@@ -20,6 +20,8 @@ for:
       - sh: curl -sflL 'https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-ssh.sh' | bash -e -
     install:
       - sh: git fetch --prune --unshallow # to fix the version dump issues
+      - sh: sudo DEBIAN_FRONTEND=noninteractive ls /etc/apt/sources.list.d/
+      - sh: sudo DEBIAN_FRONTEND=noninteractive cat /etc/apt/sources.list
       - sh: sudo DEBIAN_FRONTEND=noninteractive apt-get -y update
       - sh: sudo DEBIAN_FRONTEND=noninteractive apt-get -y install python3.7-dev libgtk-3-dev python3-pip libwebkit2gtk-4.0-dev
     before_build: