Try out releases on Travis

Author: ben

.travis.yml

@@ -0,0 +1,20 @@
+language: ruby
+before_install:
+- gem install bundler
+- bundle install
+script: bundle exec rake book:build
+deploy:
+  provider: releases
+  file:
+  - progit.epub
+  - progit.mobi
+  - progit.pdf
+  skip_cleanup: true
+  on:
+    tags: true
+  api-key:
+    secure: "l3XdupX6dT48IoTieJXrd7Yx8+KhiR2QYrNrDzT6RKxA7UyXGSP/axsVerg7OjKfIHWZgDJRVzcc2RswE+Xjw9sOY8r2h2q9uCwj8G0EqtFbtgGK0La5LB0euh0tNJN8GLFj1OdSZGY7dWWK88GXeHCua2WSify0V79R4ClIM+s="
+branches:
+  only:
+  - master
+  - /^2\.1(\.\d+)+$/