Fix bash default substitution

Closes: #165

weboffice/collabora.yml

@@ -61,7 +61,7 @@ services:
         --o:ssl.termination=true \
         --o:welcome.enable=false \
         --o:net.frame_ancestors=${OC_DOMAIN:-cloud.opencloud.test}${TRAEFIK_PORT_HTTPS:+:}${TRAEFIK_PORT_HTTPS:-} \
-        --o:net.lok_allow.host[14]=${OC_DOMAIN-cloud.opencloud.test}${TRAEFIK_PORT_HTTPS:+:}${TRAEFIK_PORT_HTTPS:-} \
+        --o:net.lok_allow.host[14]=${OC_DOMAIN:-cloud.opencloud.test}${TRAEFIK_PORT_HTTPS:+:}${TRAEFIK_PORT_HTTPS:-} \
         --o:home_mode.enable=${COLLABORA_HOME_MODE:-false}
       username: ${COLLABORA_ADMIN_USER:-admin}
       password: ${COLLABORA_ADMIN_PASSWORD:-admin}