Add automated updates

Signed-off-by: Knut Ahlers <knut@ahlers.me>

.travis.yml

@@ -0,0 +1,7 @@
+sudo: required
+
+services:
+  - docker
+
+script:
+  - bash update-version.sh

update-version.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+
+set -euo pipefail
+
+### ---- ###
+
+echo "Switch back to master"
+git checkout master
+git reset --hard origin/master
+
+### ---- ###
+
+echo "Fetching latest version..."
+LATEST=$(curl -sSLf 'https://lv.luzifer.io/catalog-api/radicale/latest.txt?p=version')
+
+echo "Found version ${LATEST}, patching..."
+sed -i "s/RADICALE_VERSION=.*$/RADICALE_VERSION=${LATEST}/" Dockerfile
+
+echo "Checking for changes..."
+git diff --exit-code && exit 0
+
+echo "Testing build..."
+docker build .
+
+echo "Updating repository..."
+git add Dockerfile
+git -c user.name='Travis Automated Update' -c user.email='travis@luzifer.io' \
+  commit -m "Radicale ${LATEST}"
+git tag ${LATEST}
+
+git push -q https://${GH_USER}:${GH_TOKEN}@github.com/luzifer-docker/radicale.git master --tags