Improve auto-update

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

.travis.yml

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

update.sh

@@ -1,5 +1,13 @@
 #!/bin/bash
-set -euxo pipefail
+set -euo pipefail
+
+### ---- ###
+
+echo "Switch back to master"
+git checkout master
+git reset --hard origin/master
+
+### ---- ###
 
 version=$(curl -s "https://lv.luzifer.io/catalog-api/wordpress/latest.txt?p=version")
 grep -q "WP_VERSION=${version} " Dockerfile && exit 0 || echo "Update required"
@@ -10,3 +18,18 @@ sed -Ei \
 	-e "s/WP_VERSION=[0-9.]+/WP_VERSION=${version}/" \
 	-e "s/WP_CHECKSUM=[a-z0-9]+/WP_CHECKSUM=${wphash}/" \
 	Dockerfile
+
+### ---- ###
+
+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 "WordPress ${version}"
+git tag ${version}
+
+git push -q https://${GH_USER}:${GH_TOKEN}@github.com/luzifer-docker/wordpress master --tags