Add travis blog update script

.travis.yml

@@ -10,3 +10,5 @@ script:
   - git clone https://github.com/phil-opp/blog_os.git
   - cp -r blog_os/blog ../blog
   - hugo
+
+after_success: bash travis-blog-update.sh

travis-blog-update.sh

@@ -0,0 +1,36 @@
+#!/bin/sh
+
+set -e
+
+# update blog if current branch is `hugo`
+[ "$TRAVIS_BRANCH" = hugo ]
+[ "$TRAVIS_PULL_REQUEST" = false ]
+
+# decrypt ssh key
+eval SSH_KEY_TRAVIS_ID=aaae456e27e9
+eval key=\$encrypted_${SSH_KEY_TRAVIS_ID}_key
+eval iv=\$encrypted_${SSH_KEY_TRAVIS_ID}_iv
+
+mkdir -p ~/.ssh
+openssl aes-256-cbc -K $key -iv $iv -in blog_os/scripts/travis-blog_os.enc -out ~/.ssh/id_rsa -d
+chmod 600 ~/.ssh/id_rsa
+
+# clone gh-pages to `deploy_blog`
+git clone --branch gh-pages git@github.com:$TRAVIS_REPO_SLUG deploy_blog
+cd deploy_blog
+
+# set git user/email
+git config user.name "travis-update-bot"
+git config user.email "travis-update-bot@phil-opp.com"
+
+# update blog
+rm -r *
+cp -r ../public/. .
+rm -r post post.html page page.html # remove per-category pages/feeds
+
+# commit
+git add --all .
+git commit -qm "Update blog to $TRAVIS_COMMIT"
+
+# push changes
+git push -q origin gh-pages