Add update-version script

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

.gitignore

@@ -0,0 +1 @@
+jq

.travis.yml

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+sudo: required
+
+services:
+  - docker
+
+script:
+  - bash update-version.sh

update-version.sh

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+#!/bin/bash
+
+set -e
+set -o pipefail
+
+HOST_OS=$(uname -s)
+
+### ---- ###
+
+echo "Switch back to master"
+git checkout master
+git reset --hard origin/master
+
+### ---- ###
+
+if ! [ -e jq ]; then
+  echo "Loading local copy of jq-1.5"
+
+  case ${HOST_OS} in
+    Linux)
+      curl -sSLfo ./jq https://github.com/stedolan/jq/releases/download/jq-1.5/jq-linux64
+      ;;
+    Darwin)
+      curl -sSLfo ./jq https://github.com/stedolan/jq/releases/download/jq-1.5/jq-osx-amd64
+      ;;
+    *)
+      echo "/!\\ Unable to download jq for ${HOST_OS}"
+      exit 1
+      ;;
+  esac
+
+  chmod +x jq
+fi
+
+### ---- ###
+
+echo "Fetching latest version..."
+LATEST=$(curl -sSLf https://index.docker.io/v1/repositories/jenkins/tags | ./jq -r '.[].name' | grep "^[0-9]\+\.[0-9]\+\(\.[0-9]\+\)\?$" | sort -Vr | head -n1)
+
+echo "Found version ${LATEST}, patching..."
+sed -i "s/^FROM.*$/FROM jenkins:${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' -c user.email='travis' \
+  commit -m "Jenkins ${LATEST}"
+git tag ${LATEST}
+
+git push -q https://${GH_USER}:${GH_TOKEN}@github.com/Luzifer/docker-jenkins.git master --tags